11 


WESTERN 

MILL  AND  SMELTER  METHODS 
OF  ANALYSIS 


(THIRD   EDITION.) 


A     Practical     Laboratory    Handbook    for  the  Assayer    and 

Chemist,    Describing    the    Methods  of   Analysis  in 

Every-day  Use  in  Western  Mills,  Smelters 

and   Custom   Assay   Offices. 


BY 

PHILIP    H.    ARGALL,    B.S.,   M.A. 

\  i 

Sometime  Assistant   Chemist  'Grant  Plant,   A.    S.    &   R.    Co. 
Assistant  Chemist  Washoe  Plant,  Anaconda  Copper  Mining  Co. 
Chemist    (student)    Metallic    Extraction    Co.'s    Works. 
Chemist  Cyanide  and  Electrum  Mining  and  Milling  Co.'s  Works, 

St.   Elmo,   Colo. 
Assistant  Chemist   Selby   Smelting  and   Lead  Co. 


1908. 
MINING     SCIENCE    PUBLISHING     COMPANY. 

(Publishers  of  Mining  Science.) 
DENVER,  COLORADO,  U.    S.    A. 


A7 


COPYRIGHT    1905 

BY 

THE     INDUSTRIAL   PRINTING     AND     PUBLISHING     CO. 
COPYRIGHT    NOW    OWNED 

BY 
THE     MINING     SCIENCE     PUBLISHING     CO. 


•>*'.  I  * '"    ' 

•  '  '       - 


CONTENTS 


CHAPTER    I. 
STANDARD    SOLUTIONS. 

Standardizing  Solutions — Potassium  Bichromate,  Potas- 
sium Permanganate,  Potassium  Ferro-cyanide,  Po- 
tassium Cyanide,  Sodium  Thiosulphate,  Ammonium 
Molybdate  7-15 

CHAPTER    II. 

SLAG    ANALYSIS. 

Determinations— Lead  Slags:  Iron,  Silica  and  Lime, 
Manganese,  Zinc,  Magnesium,  Alumina;  Copper 
Slags:  Silica  and  Iron,  Lime,  Copper;  Reverbera- 
tory  Furnace  Slags:  Silica  and  Iron,  Copper,  Lead; 
Mattes;  Conversion  Table 16-26 

CHAPTER    III. 

ORES. 

Silica,  Iron  and  Lime;  Zinc;  Manganese;  Sulphur; 
Copper  and  Lead;  Baryta;  Antimony  and  Arsenic; 
Standard  Iodine  Solution:  Modification;  Mixture 
Beds;  Alumina,  etc.;  Briquettes:  Silica  and  Iron, 
Lime  .  27-39 


CHAPTER    IV. 

COAL    AND    COKE. 

Proximate   Analysis :     Coke    40-41 

CHAPTER    V. 

OTHER  METHODS  OF  ANALYSIS. 

Antimony  and  Arsenic;  Pattenson's  Method  (modified) 
Slags,  Iron,  Lime,  Lead,  Copper;  Colorimetric,  to 
make  up  the  standard,  Copper  in  Slags  and  Tail- 
ings, Specimen  Lead  Slag  Analysis;  Specimen  Bed 
Analysis  for  Lead  Smelter;  Specimen  Briquette 
Analysis  42-53 


36483? 


CHAPTER    VI 

CYANIDE  PROCESS— DAILY  WORK. 
Titrations  of  Cyanide  Solutions;  Titration  of  Alkalinity; 
Estimation  of  Alkalies;  Manganese  in  Cyanide  So- 
lutions; Estimation  of  Free  Cyanide;  Estimation  of 
Total  Cyanide;  Estimation  of  HCN;  Estimation  of 
Ferrocyanide  by  means  of  Potassium  Permanganate; 
Estimation  of  Thio-cyantes  by  means  of  Iodine;  Es- 
timation of  Total  Cyanogen;  Estimation  of  Zinc  by 
Decomposition  with  HNO3  and  HC1;  Estimation  of 
Copper;  Estimation  of  Gold;  Estimation  of  Silver; 
Purple  of  Cassius  Test  for  Gold;  Qualitative  Detec- 
tion of  Gold;  Estimation  of  the  Reducing  Power  of 
Solution;  Estimation  of  Alkaline  Sulphides;  Esti- 
mation of  Sulphides  by  Colorimetric  Test  with 
Sodium  Nitro-Prusside;  Estimation  of  Bromo  Cya- 
nogen and  Potassium  Bromate .  54-83 


CHAPTER    VII. 

ESTIMATION     OF    OXYGEN    IN    WORKING    CYANIDE 

SOLUTIONS. 

Apparatus   Necessary;     Solutions;     Calculations;     Precau- 
tions;    Specimen  Analysis  of  Mill   Solutions 84-92 


CHAPTER    VIII. 

ORE    TESTING    BY    THE    CYANIDE    PROCESS. 
Preliminary  Tests;    Consumption   Test;     Preliminary  Ex- 
traction   Tests;      Roasting;     Modification     of     Bottle 
Test;    Percolation  Tests 93-105 


CHAPTER    IX. 

THE    ANALYSIS    OF    BRONZING    AND    BEARING    METALS. 
Bronzes;        Determination      of      Phosphorous;        Bearing 

Metals    106-110 


CHAPTER  X. 
REFINERY  METHODS. 

Mill  Slags;  Slags;  Silver  Determination  on  Anode 
Copper  by  Fire  Assay;  Bismuth  in  Metallic  Copper; 
Electrolytic  Copper  Determination 111-130 


CHAPTER    XI. 
THE    LABORATORY. 

The  Hot  Plate;  Filter  Racks;  Burette  Stand;  Distilled 
Water;  Balances;  Miscellaneous;  The  Assay  Ton 
System;  Impurities  in  C.  P.  Acids;  Hydrochloric 
Acid;  Nitric  Acid;  Sulphuric  Acid;  Ammonia;  In- 
ternational Atomic  Weights  131-144 


PREFACE. 


In  May,  1904,  I  presented,  in  part  fulfillment  of  the 
requirements  for  the  degree  Master  of  Arts  in  the 
University  of  Colorado,  a  thesis  entitled  "Smelter  and 
Mill  Methods  of  Analysis  in  Use  in  the  West."  This 
thesis  was  later  published  in  Volume  II.,  No.  i,of  the 
University  Studies,  and  though  primarily  intended  for 
the  use  of  students  in  the  University,  it  has  been  found 
to  be  of  considerable  help  to  practical  chemists  in  all 
parts  of  the  West. 

This  treatise,  revised  and  enlarged  from  the  thesis, 
is  intended  for  the  use  of  practical  chemists  and  assayy 
ers,  and  presupposes  a  thorough  knowledge  of  chem- 
istry. Hence  no  attempt  is  made  to  explain  the  nature 
of  the  chemical  reactions  that  take  place,  a  simple  and 
clear  outline  alone  is  given.  The  methods  of  analysis 
given  are  those  in  every-day  use  in  lead  and  copper 
smelters  and  in  cyanide  mills. 

Acknowledgment  is  due  Mr.  J.  E.  Clennell  for  the 
description  of  a  number  of  determinations  in  connection 
with  the  cyanide  process  from  his  paper  "Analytical 
Work  in  Connection  With  the  Cyanide  Process/'  which 
was  read  before  the  Institute  of  Mining  and  Metallurgy 
in  London  on  May  21,  1903 ;  and  to  Mr.  Philip  Argall 
for  much  of  the  material  in  the  chapter  on  "Ore  Test- 
ing by  the  Cyanide  Process." 

Other  authors  have  been  freely  consulted  and  due 
credit  is  given  when  any  method  so  obtained  has  been 
used  in  this  treatise. 

To-day  the  metallurgical  chemist  almost  entirely 
relies  on  volumetric  methods  for  the  analytical  deter- 
minations required  in  metallurgical  work.  The  opera- 
tions of  mill  and  smelter  are  being  more  and  more 
directed  according  to  the  results  obtained  in  the  lab- 
oratory and  the  metallurgical  chemist  is  now  required  to 


6         MILL   AND    SMELTER    METHODS. 

make  daily  a  number  of  determinations  that  would 
appall  his  predecessor  of  even  a  few  years  ago.  -The 
time  allowed  for  making  individual  determinations  is 
also  being  steadily  reduced.  Hence,  'the  chemist  is 
debarred  from  making  the  slower,  but  possibly  more 
accurate,  gravimetric  determinations.  He  is  driven, 
therefore,  to  using  volumetric  methods  as  far  as  possi- 
ble. The  speed  and  the  comparatively  small  amount  of 
attention  required  by  individual  assays  in  volumetric 
work  also  makes  for  the  adoption  of  these  methods.  A 
few  years  ago  furnace  and  gravimetric  methods  of 
analysis  were  standard;  today,  except  for  gold  and  sil- 
ver, volumetric  methods  are  used  almost  exclusively. 

The  standard  solutions  used  are  made  up  in  large 
quantities  at  a  time,  and  are  kept,  as  far  as  possible,  in  a 
cool,  dark  place.  Most  of  the  solutions  used  maintain 
their  standard  for  a  considerable  length  of  time. 

Selby  Works,  March  ist,  1905. 


The  second  edition  of  this  book  has  made  possible 
the  correction  of  errors  in  the  former  edition  and  has 
enabled  me  to  add  some  new  methods  and  to  include 
others  overlooked  in  the  first  instance.  Very  little  that 
is  actually  new  has  turned  up  in  the  ordinary  smelter 
routine  in  the  past  three  years,  but  a  gradual  uniform- 
ity in  methods,  which  did  not  exist  then,  has  come 
about,  and  in  changing  from  one  laboratory  to  another 
now  one  has  no  new  methods  to  learn. 

The  first  edition  of  this  work  was  very  favorably 
received,  and  I  hope  that  this  will  be  no  less  so,  for, 
while  many  shortcomings  will  be  found,  I  believe  that 
the  ground  covered  has  been  thoroughly  gone  over. 

Selby  Works,  September,   1908. 


CHAPTER  1. 


Standard    Solutions. 


The   following  standard   solutions  are  in   general 
use  in  the  lead  and  copper  smelters  of  the  West: 


Amount  of  Salt  in 

Name  of  Solution.             One  Litre. 

Approximate 

Used  for 

Theoretical. 

Practical 

.    Standard. 

Determining. 

Potassium  Bichromate  —  4.381 

4.4 

lcc=r.005  Fe. 

Fe. 

Sodium   Thiosulphate  19.  59 

20.0 

lcc=.005  Cu. 

As,  Cu,  I,  Sb. 

Mn,  CaO. 

Potassium  Permanganate.  5.643 

5.8 

lcc=.005  CaO. 

Fe,  Sb. 

Potassium  Ferrocyanide.  . 

22.5 

lcc=.005  Zn. 

Zn. 

Ammonium  Molybdate  

4.28 

lcc=.005  Pb. 

Pb. 

Potassium  Cyanide  

44.5 

lcc=.010  Cu. 

Cu. 

Oxalic   Acid  11.25 

11.46 

lcc=lcc  K  Mn04. 

Mn. 

=lcc  .01  Fe. 

Potassium  Sulphocyanate.  8.981 

10.0 

lcc=.01  Ag. 

Ag,  As, 

Barium  Chloride  76.  25 

76.25 

lcc=.01  S. 

S. 

Ammonium  Oxalate 40  grams    per    litre 

Barium  Chloride 20 

Mercuric  Chloride 50      " 

Sodium    Phosphate 100      "         "        " 


Stannous  chloride,  made  by  saturating  hydrochloric 
acid  with  tin,  diluting  with  an  equal  volume  of  water, 
and  adding  a  slight  excess  of  water  from  time  to  time. 
A  strip  of  metallic  tin  is  kept  in  the  bottle. 

From  the  potassium  permanganate  solution  above 


8          MILL  AND  SMELTER  METHODS. 

I  cc.  equals  .005  Lime,  the  following  comparison  is 
deduced : 

100  CaO=253-3  ammonium  oxalate. 

100  CaO=2O3.3  oxalic  acid. 

100  Fe.  =700.0  ferrous  ammonium  sulphate. 

All  of  these  solutions,  except  potassium  cyanide, 
keep  well  if  kept  in  dark  bottles ;  Messrs.  Walter  M. 
Gardner  and  B.  North*  found  that  a  solution  of 
potassium  permanganate  kept  its  strength  for  twelve 
months  and  that  a  solution  of  ammonium  oxalate 
deteriorates  at  the  rate  of  I  %  in  two  weeks. 

In  actual  practice  these  solutions  are  made  to  read 
i  cc.=.oo5,  so  that  the  reading  will  be  direct  on  \ 
gram  of  ore  or  slag. 

Impurities  in  the  chemicals,  even  in  the  so-called 
C~  P.,  as  well  as  dust  and  organic  matter  (sometimes 
in  the  water  obtained  in  the  condensation  of  boiler 
steam,  and  due  to  the  use  of  organic  boiler  com- 
pounds) generally  affect  the  solutions  more  or  less, 
hence  it  is  well  to  let  them  stand  a  few  days  before 
using.  If  the  laboratory  possesses  a  suction  pump, 
the  flask  containing  the  newly  made  solution  may  be 
fitted  with  a  cork  containing  two  pieces  of  glass 
tubing,  one  piece  reaching  to  the  bottom  of  the  flask 


*  Journal  of  the  Society  of  Chemical  Industry,  June  15, 
1904,   page    599. 


MILL    AND    SMELTER    METHODS.         9 

and  the  other  ending  just  above  the  surface  of  the 
liquid,  the  latter  piece  being  connected  to  the  pump  by 
a  rubber  tube,  air  may  be  drawn  through  the  solution 
over  night,  thoroughly  mixing  it.  These  solutions 
should  be  made  up  in  quantities  of  not  less  than  four 
litres,  and  in  large  laboratories,  especially  where  it 
is  necessary  to  let  them  stand  a  few  days  before  using, 
one  flask  should  be  standing  while  its  duplicate  is 
in  use. 

The  difference  between  the  theoretical  and  prac- 
tical columns  in  the  table  is  due  to  impurities  in  the 
chemicals  and  in  the  water  used. 


Standardizing    Solutions. 


Potassium  Bichromate. 

Weigh  out  a  piece  of  C.  P.  iron  wire  approxi- 
mately .200  gram.  Cut  the  wire  into  small  pieces, 
place  in  a  beaker  and  pour  15  cc.  cone,  hydrochloric 
acid  and  15  cc.  boiling  distilled  water  over  it  and  heat 
until  dissolved.  Dilute  with  100  cc.  of  water  and 
boil.  Remove  from  the  heat  and  while  still  hot  reduce 
with  a  few  drops  of  stannous  chloride  solution,  stir- 
ring vigorously.  When  quite  cold  add  20  cc.  of  a 
strong  solution  of  mercuric  chloride  and  stir  well. 


io       MILL   AND    SMELTER    METHODS. 

The  solution  should  now  look  white  and  silky  from 
the  presence  of  mercurous  chloride,  and  is  ready  for 
titration. 

Titrate  with  the  standard  solution  using  a  solu- 
tion of  potassium  ferricyanide  as  an  indicator.  Divide 
the  weight  of  iron  taken  by  the  number  of  cc/s  used, 
then  the  quotient  will  represent  the  amount  of  iron 
in  the  ferrous  condition  which  I  cc.  of  the  solution 
is  capable  of  oxidizing.  . 

The  mercuric  chloride  solution  is  simply  a  con- 
centrated solution  of  the  salt  in  distilled  water. 

The  ferricyanide  indicator  is  prepared  by  adding 
two  or  three  grams  of  the  salt  to  200  cc.  of  distilled 
water,  and  should  be  made  fresh  daily. 

Potassium  Permanganate. 
Three  methods  are  in  general  use: 

(a)  By  iron  wire. 

(b)  By  oxalic  acid. 

(c)  By  ferrous  ammonium  sulphate. 

Comparing  the  following  equations: 
io  FeS04  +  2  KMn04  +  8  H2SO4  =  5  Fe2(SO4)8  + 

K2SO4+2  MnSO4+8  H2O     and, 
5(H2C2O4,  2  H2O)+2  KMnO4+3  H2SO4=io  CO2+ 

2  MnSO4+K2SO4+i8  H2O. 

it  will  be  seen  that  two  equivalents  of  iron  .require 
the  same  amount  of  permanganate  solution  for  oxida- 


MILL   AND    SMELTER    METHODS.        n 

tion  as  one  equivalent  of  oxalic  acid,  or,  2/56  iron  is 
equal  to  126  oxalic  acid,  i.  e.,  as  8:9.  Taking  oxalic 
acid,  therefore,  we  simply  multiply  the  weight  taken 
by  8/9  to  find  the  'equivalent  in  iron. 

The  composition  of  ferrous  ammonium  sulphate  is 
Fe(NH4)2(SO4),6H2O,  the  molecular  weight  is  392, 
of  which  56,  or  1/7,  is  iron. 

(a)  To  Standardize  with  Iron  Wire. — Weigh  out 
approximately  .200  gram  of  iron  wire,  cut  it  into  small 
pieces  and  place  in  a  flask.     Pour  upon  it  20  cc.  cold 
water  and  5  cc.  cone,  sulphuric  acid  and  heat  until  all 
the  iron  is  dissolved.     When  completely  dissolved  add 
20  to  30  cc.  of  hot  water  and  a  spoonful  of  granulated 
zinc  (aluminum  foil  is  just  as  good)  and  boil  for  a  few 
minutes.     Remove  •  and  cool  the  beaker  and  test  the 
solution   with   potassium   sulphocyanide.     If   no   pink 
colpration  is  shown  add  100  cc.  cold  water,  stir,  allow 
the  zinc  to  settle,  decant  the  solution  and  wash  with 
water,  being  careful  that  none  of  the  zinc  passes  over. 
The  solution  is  now  ready  for  titration  with  the  per- 
manganate  solution.     Run   in   rapidly,   with   constant 
stirring,  until  a  faint  pink  appears. 

(b)  To   Standardize   with   Oxalic   Acid. — Weigh 
out  about  |  gram  of  the  pure  acid,  which  has  been 
kept  in  a  well  stoppered  bottle.     Dissolve  in  a  No.  3 
beaker  in  about  350  cc.  of  boiling  water.     In  another 
beaker  place  50  cc.  cold  water  and  add  to  it  20  cc. 


12       MILL   AND    SMELTER    METHODS. 

strong  sulphuric  acid ;  mix  by  shaking  around  gently, 
then  pour  this  hot  acid  into  the  oxalic  acid  and  titrate 
at  once  with  the  volumetric  solution. 

(c)  To  Standardize  with  Ferrous  Ammonium 
Sulphate. — Coarsely  powder  about  3  grams  of  the  salt 
in  a  porcelain  mortar,  weigh  out  about  2.1  grams  and 
dissolve  it  in  250  cc.  cold  water.  Add  20  cc.  sulphuric 
acid  ( i  part  acid,  5  parts  cold  water)  and  when  the 
salt  has  completely  dissolved  titrate  with  the  volu- 
rnetric  solution. 

Potassium  Ferrocyanide. 

Ignite  in  a  porcelain  crucible  about  3  grams  of 
C.  P.  zinc  oxide.  Cool  in  a  dessicator.  When  cold 
weigh  out  as  rapidly  as  possible  .250  gram,  place  in  a 
No.  2  beaker  and  add  25  cc.  boiling  distilled  water  and 
5  cc.  hydrochloric  acid.  Warm  until  completely  dis- 
solved. Add  7  grams  ammonium  chloride  and  15  to 
25  grams  test  lead,*  dilute  to  200  to  225  cc.  and  boil. 

Take  off  the  hot  plate  when  boiling,  add  I  to  2  cc. 
of  a  concentrated  solution  of  sodium  sulphite  (the 
solution  should  smell  of  sulphur  di-oxide)  and  titrate, 
using  a  solution  of  uranium  acetate  as  an  indicator. 


*  The  addition  of  the  lead  is  not  necessary  here,  but 
since  lead  is  invariably  used  to  precipitate  copper  when 
testing  for  zinc  ores  (Low's  method)  it  is  desirable  to  have 
the  same  conditions  here. 


MILL   AND    SMELTER    METHODS.        13 

The  writer  has  found  it  a  good  plan  to  divide  the 
solution  before  adding  the  sodium  sulphite,  leaving  20 
to  30  cc.  on  the  lead  in  the  beaker,  and  to  this  part 
adding  the  sodium  sulphite.  Titrate  the  other  portion 
rapidly  until  a  good  end  reaction  is  reached,  then  pour 
in  the  other  part,  lead  and  all,  rinse  carefully  and  com- 
plete the  titration  slowly.  This  precaution  prevents 
running  past  the  end  point. 

The  uranium  acetate  indicator  is  prepared  by  dis- 
solving sufficient  uranium  acetate  in  water  to  give  a 
pretty  strong  solution  and  clarified  by  adding  a  few 
drops  of  acetic  acid. 

Or,  weigh  carefully  about  0.2  gram  of  pure  zinc 
and  dissolve  in  10  cc.  of  strong  HC1,  using  a  400  cc. 
covered  beaker.  Dilute  and  put  in  a  piece  of  litmus 
paper  and  make  faintly  alkaline  with  ammonia. 
Acidify  with  HC1  and  then  add  3  cc.'s  in  excess  of 
the  strong  acid.  Dilute  to  300  cc.  and  heat  nearly 
to  boiling  and  titrate  the  hot  solution  with  the  ferro- 
cyanide  solution,  proceeding  as  above. 

[Note.- — The  end  point  is  always  passed  by  a  test 
or  two  and  the  burette  reading  must  be  corrected  ac- 
cordingly.] 

Potassium  Cyanide. 

Weigh  out  a  piece  of  copper  foil,  approximately 
.250  gram,  place  in  a  beaker  and  dissolve  in  5  cc. 
strong  nitric  acid.  Boil  off  the  red  fumes  and  cool  by 


14       MILL   AND    SMELTER    METHODS. 

dipping  in  cold  water.  Add  20  cc.  cold  water,  then 
10  cc.  strong  ammonia,  stir  and  cool.  Titrate  with 
the  volumetric  solution  of  potassium  cyanide. 

Sodium  Thiosulphate. 

Weigh  out  .200  gram  copper  foil,  and  dissolve  it  in 
a  beaker  in  5  cc.  strong  nitric  acid.  Boil  off  the  red 
fumes  carefully  to  avoid  trouble  later  on  when  any 
nitrous  acid  present  would  liberate  iodine.  Remove 
from  the  heat  and  add  15  cc.  of  water  and  from  6  to  7 
grams  of  zinc  acetate  and  boil  for  a  few  minutes. 
Remove  from  the  heat  and  allow  to  become  quite 
cold,  then  add  50  cc.  cold  water  and  from  3  to  4  grams 
of  potassium  iodide,  stirring  until  dissolved.  Cuprous 
iodide  will  be  precipitated  and  iodine  liberated. 

2  Cu(C2H,O2)2+4  KI=Cu2I2+4  KC2H,O2+I2. 

The  free  iodine  is  soluble  in  potassium  iodide  and 
colors  the  solution  brown.  Titrate  at  once  with  the 
thiosulphate  solution  until  the  brown  tinge  has  become 
weak,  then  add  about  5  cc.  of  starch  solution  and 
continue  the  titration  until  the  blue  color  disappears, 
leaving  the  solution  milky  and  somewhat  yellow. 

The  starch  solution  is  prepared  by  adding  ^  gram 
of  starch  to  200  cc.  boiling  distilled  water  and  stir- 
ring. A  new  solution  should  be  made  every  few  days. 


MILL   AND    SMELTER    METHODS.        15 

Ammonium  Molybdate. 

Weigh  .200  gram  of  C.  P.  anhydrous  lead  sul- 
phate and  place  in  a  No.  2  beaker.  Add  10  grams  of 
ammonium  acetate  and  100  cc.  of  boiling  water.  Heat 
until  the  lead  sulphate  is  dissolved.  Titrate  boiling 
hot  with  the  molybdate  solution,  using  a  solution  of 
tannio  acid  as  an  indicator. 

The  tannic  acid  solution  is  prepared  by  adding  200 
cc.  of  water  to  1/20  gram  of  tannic  acid. 


16       MILL   AND    SMELTER    METHODS. 


CHAPTER   II. 


Slag  Analysis. 


The  composition  of  a  slag  in  any  given  smelting 
operation  has  probably  a  greater  influence  on  the 
success  of  the  process  than  any  other  single  factor, 
regarded  either  from  a  technical  or  financial  stand- 
point. 

Smelting  may  be  regarded  as  the  fusion  or  reduc- 
tion of  an  ore  or  ores,  so  that  the  resulting  metal  or 
matte,  by  reason  of  its  greater  specific  gravity,  may 
sink  through  the  fused  gangue  and  be  collected  for 
further  purification  freed  from  the  earthy  metals 
which  form  the  slag.  In  order  that  this  separation 
may  be  complete  and  perfect,  the  slag  must  fuse  at 
a  temperature  as  near  the  fusing  point  of  the  metal 
as  possible,  and  in  most  cases,  the  more  fluid  the  slag, 
and  the  lower  its  specific  gravity,  the  better  it  is.  In 
the  lead,  copper  and  iron  industry,  the  slags  are 
invariably  complex  silicates ;  that  is,  a  silicate  of 
numerous  bases.  The  ratio  of  acid  to  base  has  an 
exceedingly  important  influence  on  the  perfect  separa- 
tion of  the  metals  from  the  slag,  affecting,  as  it  does, 
the  specific  gravity,  the  fusibility,  the  influence  on  the 
furnace  walls  and  the  influence  on  the  oxide  of  the 
metal  to  be  separated. 


MILL   AND    SMELTER    METHODS.        17 

In  general  it  has  been  found  that  "singulo- 
silicates"  are  the  most  fluid,  fuse  at  the  lowest  temper- 
ature and  are  most  commonly  used  where  econom- 
ically possible.  (A  slag  in  which  the  ratio  of  the 
oxygen  combined  in  the  silica  is  to  the  oxygen  com- 
bined in  the  bases  as  i :  i  is  called  a  singulo-silicate. ) 

It  has  been  found  that  if  a  slag  be  suddenly  chilled 
either  by  pouring  into  water,  or  upon  a  cold  piece  of 
steel,  or  even  by  dipping  a  cold  steel  bar  into  the 
fluid  slag  and  quickly  removing  it  with  its  adhering 
slag,  the  slag  so  treated  has  a  vitreous  lustre  and 
decomposes  rapidly  and  completely  with  acids.  If, 
however,  it  is  allowed  to  cool  slowly,  as  it  would 
under  ordinary  circumstances,  it  is  no  longer  decom- 
posed by  acids,  but  requires  fusion  with  alkaline 
carbonates.  With  singulo-silicates  the  decomposition 
is  perfect  when  the  slag  is  chilled,  but  as  the  slags 
become  more  acid  they  become  more  difficult  to 
decompose,  and  when  slags  approach  40%  silica  the 
decomposition  is  no  longer  satisfactory. 

In  all  lead  smelters  at  least  one  sample  of  slag  is 
analyzed  daily,  and  from  the  analysis  the  fluxes  are 
adjusted.  This  slag  analysis  is  the  first  thing  taken 
up  by  the  chemist  when  he  arrives  at  the  plant  in  the 
morning,  and  since  the  results  are  expected  by  10  a.  m. 
very  rapid  methods  are  required. 

The  figures  generally  required  on  lead  slags  are 
silica,  iron,  lime,  zinc,  manganese,  magnesium  and 
alumina;  lead  and  silver  are  determined  by  the  fire 


i8       MILL   AND    SMELTER    METHODS. 

assay.*  A  separate  portion  of  J  gram  is  weighed  out 
for  iron,  manganese,  zinc  and  aluminum ;  silica  and 
lime  are  determined  on  one  weighing. 

On  copper  slags  silica,  iron  and  lime  are  the  only 
elements  usually  called  for,  so  silica  and  iron  are 
made  on  one  weighing  and  lime  on  a  separate  one. 

The  slag  is  usually  delivered  to  the  chemist  ground 
and  screened,  so  that  he  may  weigh  up  at  once. 


Determinations — Lead    Slags. 

Iron. 

To  -J  gram  of  slag  add  20  cc.  boiling  water  and  15 
cc.  strong  hydrochloric  acid.  Boil  until  all  action 
ceases.  Now  add  3  drops  of  stannous  chloride  solu- 
tion and  allow  to  cool.  When  cold  add  15  cc.  mercuric 
chloride  to  neutralize  the  excess  tin.  Titrate  with 
bi-chromate  solution,  using  the  potassium  ferricyanide 
indicator. 

This  method  of  the  complete  solution  of  the  slag 
in  water  and  hydrochloric  acid  is  of  value  in  another 
way,  as  it  gives  an  indication  of  incomplete  reduction 
in  the  furnace — i.  e.,  if  the  solution  has  a  yellow  color 
it  shows  that  some  of  the  iron  is  present  in  the  ferric 
state,  and  when  this  is  the  case  it  may  be  necessary 
to  give  an  increased  amount  of  fuel ;  such  a  fact 
should  be  noted  on  your  report. 


*  It    has   recently   become   the    practice   in    Colorado    to 
make  wet  leads  also  on  slags. 


MILL   AND    SMELTER    METHODS.        19 

Silica  and  Lime. 

Weigh  into  a  No.  3  R.  B.  casserole  -J  gram  of 
slag  and  moisten  it  with  water.  Then  add  4  to  5  cc. 
hydrochloric  acid  and  stir  with  a  glass  rod  (keep  stir- 
ring while  adding  the  acid  in  order  to  prevent  the 
silica  gelatinizing  and  forming  lumps.)  Evaporate 
to  dryness  on  the  hot  plate,  being  careful  to  avoid 
"spitting."  Take  up  with  5  cc.  hydrochloric  acid  and 
5  cc.  water,  and  boil.  Dilute,  filter  into  a  beaker 
containing  3  cc.  of  nitric  acid.  Burn  the  filter  paper 
in  a  porcelain  crucible  in  the  muffle,  cool  and  weigh 
as  silica. 

To  the  filtrate  acid  with  nitric  acid,  add  ammonia 
until  all  the  iron  is  precipitated :  re-dissolve  the  iron 
in  oxalic  acid  and  boil.  Filter  off  the  calcium  oxalate 
and  wash  carefully  with  hot  water.  Put  the  filter 
paper  containing  the  calcium  oxalate  in  a  beaker ; 
half  fill  it  with  hot  water  and  add  10  cc.  dilute  sul- 
phuric acid  warm  and  titrate  with  permanganate.  It 
will  be  observed  that  no  nitric  acid  is  used  during  the 
first  evaporation ;  this  to  avoid  the  exidation  of  the 
sulphur  which  is  combined  in  the  slag  as  a  sulphide, 
and  which  by  treatment  with  hydrochloric  acid  alone 
is  eliminated  as  hydrogen  sulphide.  If  the  sulphur 
were  oxidized  to  sulphuric  acid,  some  barium  sulphate 
would  be  formed,  and  remaining  with  silica,  make 
the  result  too  high. 

The  nitric  acid  is  used  in  the  second  stage  to 
oxidize  the  iron. 


20       MILL   AND    SMELTER    METHODS. 

There  is  invariably  a  small  amount  of  carbon  .in 
the  slag  which  will  make  the  silica  look  dark  before 
ignition,  but  it  burns  off  in  the  muffle. 

Care  must  be  taken  in  the  evaporation  to  dryness 
not  to  heat  too  strongly;  sometimes  the  iron  when 
heated  too  strongly  becomes  oxidized  to  Fe2O3  and 
obstinately  refuses  to  dissolve,  in  which  case  a  new 
determination  is  necessary.  It  will  be  noticed  that 
the  technical  term  "silica"  embraces  all  that  is  insolu- 
ble in  acids. 

Lime  in  Slags. 

A  better  method  is  the  following:  To  4  gram 
of  slag  in  a  casserole  add  a  pinch  of  potassium  chlorate, 
moisten  with  a  little  water  and  add  4  cc.  of  strong 
hydrochloric  acid.  Evaporate  to  dryness.  Take  up 
in  ammonia  water,  first  adding  about  5  grams  of 
ammonium  chloride.  Boil  well.  Filter  through  a 
fluted  filter  paper.  Redissolve  the  ppt.  and  again 
precipitate  with  ammonia  filter  and  add  the  filtrate  to 
that  obtained  in  the  first  filtration.  Wash  well,  heat 
to  boiling  and  ppt.  with  hot  ammonium  oxalate, 
and  proceed  as  before. 

Manganese. 

Weigh  out  in  a  No.  2  beaker  one-half  gram  of  slag 
and  treat  with  20  cc.  water  and  5  cc.  nitric  acid.  Boil. 
Dilute  with  hot  water,  add  enough  zinc  oxide  emulsion 
to  neutralize,  and  titrate  with  potassium  permangan- 
ate solution.  Since  this  solution  is  standardized  with 


MILL   AND    SMELTER    METHODS.       21 

iron  we  have  simply  to  multiply  by  165  divided  by  560 
equals  .2946  to  obtain  the  value  in  manganese. 

Another  method  is  to  add  5  cc.  nitric  acid  and 
4  to  5  cc.,  hydrochloric  acid  and  boil  in  a  casserole 
until  decomposed.  Now  add  4  to  5  cc.  sulphuric 
acid  and  evaporate  carefully  to  dryness.  Take  up  with 
water  and  boil  for  ten  minutes,  then  transfer  to  a 
beaker,  neutralize  with  ammonia,  then  make  slightly 
acid  with  sulphuric.  Now  add  the  zinc  emulsion  and 
proceed  as  before. 

Zinc. 

To  -J  gram  of  ore  in  a  No.  3  R.  B.  casserole  add 
10  cc.  of  chlorate  mixture  (a  saturated  solution  of  po- 
tassium chlorate  in  nitric  acid)  and  evaporate  slowly 
to  dryness.  Now -add  10  grams  of  ammonium  chlo- 
ride crystals  and  20  cc.  of  ammonia,  boil,  filter  and 
wash  with  ammonia  and  then  with  water.  To  the  ni- 
trate add  a  small  piece  of  litmus  paper  and  make  the 
solution  acid  with  hydrochloric  acid  and  then  add  5 
cc.  in  excess.  Now  add  2  to  3  grams  of  test  lead  and 
boil.  Titrate  hot  with  the  potassium  ferrocyanide  so- 
lution, using  the  uranium  acetate  indicator.  Add 
about  3  cc.  of  the  sodium  sulphite  solution  before  ti- 
trating. (See  standardizing  the  solution.) 

Some  chemists  evaporate,  to  dryness  first  with  ni- 
tric acid  and  then  take  up  and  boil  with  nitric  acid, 
adding  a  pinch  of  potassium  chlorate,  this  method  giv- 
ing steady  results. 


22       MILL   AND    SMELTER    METHODS. 

Sources  of  error  in  the  ferrocyanide  titration 
method  for  zinc — losses  may  result  from :  * 

1.  Volatilization  of  zinc  as  the  chloride. 

2.  Recombination  of  zinc  with  silica. 

3.  Imperfect  decomposition  by  acids. 

4.  Occlusion  by  ferric  hydroxide,  .etc. 

5/  The  use  of  hydrogen  sulphide  for  separating 
Cu.  Cd.,  etc. 

6.  Failure  to  make  the  final  titration  under  the 
same  conditions  as  in  standardizing. 

7.  Insufficient  dilution  of  the  solution. 

8.  Too   great   haste   in   titrating,   especially   with 
cold  solutions.    On  the  other  hand,  results  may  be  too 
high  owing  to: 

9.  The  presence,  in  the  solution,  of  Cd.  Cu.  Sb. 
Mn.  Al.  or  some  organic  acid,  as  tartaric,  oxalic,  etc. 

10.  The   decomposition   of   the   ferrocyanide   solu- 
tion by   Cl.   Br.,   nitrous   oxides,   hydrogen   peroxide, 
etc. 

11.  The  addition  of  an  inordinate  excess  of  acid 
to  the  solution. 

12.  The  use  of  an  incorrectly  standardized  solu- 
tion of  ferrocyanide. 

Magnesium. 

To  |  gram  of  slag  add  15  cc.  water,  then  10  cc. 
hydrochloric  acid  and  5  cc.  nitric  acid,  boil,  precipi- 
tate the  iron  with  ammonia  and  add  5  cc.  bromine 


*  George    Waring,    Jour.    Am.    Chem.    Soc.,    Vol.    XXVI., 
Jan.,   1904. 


MILL   AND    SMELTER    METHODS.       23 

water  (or  hydrogen  peroxide)  and  filter.  The  iron 
is  then  dissolved  •  with  5  cc.  of  hydrochloric  acid,  di- 
luted, and  again  precipitated  with  ammonia  and  bro- 
mine as  before.  The  filtrates  from  the  two  precipi- 
tates are  then  combined  and  boiled.  Ammonium  oxa- 
late  is  now  added  to  precipitate  the  lime,  which  is 
then  filtered  off.  The  filtrate  is  boiled  to  a  small  bulk 
and  5  cc.  sodium  phosphate  solution  added  and  placed 
in  a  flask  under  running  water  to  cool.  When  quite 
cold  add  20  cc.  ammonia  and  shake  for  15  minutes 
when  all  the  magnesium  phosphate  is  precipitated. 
Filter,  wash  with  cold '  dilute  ammonia,  burn  and 
weigh. 

Alumina. 

Weigh  out  in.  a  No.  3  R.  B.  casserole -J  gram  of 
slag  and  treat  as  if  for  silica,  but,  on  filtering,  do 
not  add  nitiric  acid  to  the  filtrate.  This  will  give  yo.. 
a  check  on  your  silica. 

Wash  the  filter  paper  carefully  with  dilute  hydro- 
chloric acid  and  then  with  water  before  removing. 
Then  to  the  filtrate  add  ammonia  until  the  solution 
becomes  dark  red  in  color,  but  contains  no  precipi- 
tate. Now  add  3  cc.  hydrochloric  acid  and  20  cc. 
sodium  phosphate  solution,  constantly  stirring;  then 
add  50  cc.  sodium  thiosulphate  solution  and  10  cc. 
of  99.5%  acetic  acid.  Heat  to  boiling  and  boil  for 
30  minutes ;  filter  rapidly,  wash  with  hot  water,  burn 
in  a  porcelain  crucible  and  weigh  as  aluminum  phos- 


24       MILL   AND    SMELTER    METHODS. 

phate,  which,  multiplied  by  .41847,  gives  the  weight 
of  AL2O3. 

It  is  necessary  in  burning  off  the  precipitate  to 
burn  at  a  low  temperature,  otherwise  the  aluminum 
phosphate  will  fuse. 

Copper  Slags. 

On  copper  blast  furnace  slags,  as  a  general  rule, 
only  silica,  iron  and  lime  are  required.  Hence  only 
two  weighings  are  required;  one  for  silica  and  iron, 
one  for  lime. 

Silica  and  Iron. 

Weigh  into  a  No.  3  R.  B.  casserole  -J  gram  of  the 
slag  and  treat  it  essentially  as  in  the  case  of  a  lead 
slag.  Do  not  oxidize  the  filtrate  from  the  silica,  how- 
ever, but  heat  it  to  boiling,  reduce  with  stannous  chlo- 
ride, cool  and  titrate  with  the  bichromate  solution. 
Lim(e. 

To  -J  gram  of  the  slag  in  a  No.  2  beaker  add  20  cc. 
hot  water,  10  cc.  hydrochloric  acid  and  a  pinch  of  po- 
tassium chlorate.  Stir  carefully,  and  see  that  no  slag 
is  allowed  to  stick  to  the  bottom  of  the  beaker.  Boil 
for  a  few  minutes,  then  remove  from  the  heat  and  pre- 
cipitate the  iron,  etc.,  with  ammonia.  Boil,  filter  off 
the  precipitate,  and  place  the  filtrate  on  the  hot  plate 
to  boil.  When  boiling  precipitate  the  lime  with  am- 
monium oxalate,  allow  to  settle,  filter  and  wash  care- 
fully with  hot  water.  Place  the  filter  paper  and  its 
contents  in  a  beaker,  half  fill  with  warm  water  and 


MILL   AND    SMELTER    METHODS.       25 

add  10  cc.  of  dilute  sulphuric  acid,  boil    and    titrate 
hot  with  the  permanganate  solution. 

Copper. 

To  i  gram  of  the  slag  in  a  small  beaker  add  20  cc. 
water  and  10  cc.  of  nitric  acid :  place  on  the  hot  plate 
and  boil  gently  until  the  fumes  cease;  remove,  cool, 
precipitate  the  iron  with  ammonia  and  titrate  with 
the  potassium  cyanide  solution. 

Reverberator/    Furnace   Slags. 

On  these  slags  silica,  iron,  copper  and  lead  are 
usually  required.  Ordinarily  the  copper  and  lead 
values  are  so  low  that  they  will  not  injure  the  crucible 
if  fused  direct. 

Silica  and  Iron. 

Fuse  -J  gram  of  the  slag  in  a  silver  crucible  with 
about  3  grams  of  potassium  hydroxide.  When  cold, 
remove  the  fused  mass  with  hot  water  arid  evaporate 
to  dryness  in  a  casserole  after  adding  15  cc.  of  hydro- 
chloric acid.  Take  up  in  water  and  hydrochloric  acid 
and  proceed  as  before. 

Copper. 

As  given  under  copper  slags. 
Lead. 

To  i  gram  of  slag  in  a  small  beaker,  add  15  cc.  of 
nitric  acid  and  10  ec.  of  sulphuric  acid  and  heat  un- 
til dense  white  fumes  of  SO3  are  given  off.  Remove 
from  the  heat  and  allow  to  become  quite  cold.  Add 
100  cc.  of  cold  water  and  filter.  Wash  the  lead  sul- 
phate from  the  filter  paper  into  the  original  beaker, 


26       MILL   AND    SMELTER   METHODS. 

add  10  grams  of  ammonium  acetate,  boil  and  titrate 
hot  with  the  molybdate  solution. 


Mattes. 

Matte,  roasted  matte,  fused  ore,  etc.,  are  treated  in 
the  same  way  as  slags.  The  insoluble  residue  will  in 
most  cases  have  to  be  fused  in  the  silver  crucible  with 
potassium  hydroxide,  or  in  a  platinum  crucible  with 
alkaline  carbonates.  All  these  substances  will  contain 
copper  and  lead,  and  care  must  be  taken  to  see  that 
they  are  removed  before  fusion. 

The  chemist  is  now  ready  to  make  his  report  to 
the  metallurgist,  and  since  the  elements  found  must 
be  reported  as  oxides,  the  following  conversion  table 
will  prove  useful.  Any  Pb  ore  which  has  been  sin- 
tered during  a  roasting  process  requires  an  HF  lead 
except  in  case  SiO2  is  not  present. 

CONVERSION    TABLE. 
Fex  1.29=  FeO 


Mnx  i.29=MnO 
Zn  x  1.25  =  ZnO 
Cu  x  1.25  =  CuO 
Pbxi.oS  =  PbO 

S  x  2.50  =  SO3 
As  x  1.32  =  As2O3 
Sbx  i.27=Sb2O4 

S  x  747  =  PbS 


MILL   AND    SMELTER    METHODS.       27 


CHAPTER  III. 


Ores. 


The  figures  called  for  on  ores  will,  of  course,  vary 
with  the  nature  of  the  ores,  but  the  following  are  the 
elements  that  the  metallurgist  requires  to  know  about : 
Silica,  iron,  lime,  zinc,  copper,  sulphur,  lead,  baryta, 
antimony  and  arsenic. 

True  Silica. 

True  silica  is  the  expression  used  to  distinguish 
the  silica  of  ordinary  smelter  parlance  (meaning, 
really,  that  which  is  insoluble  in  acids)  from  the  actual 
silica. 

On  ores,  briquettes,  etc.,  fuse  in  a  silver  crucible 
about  two-thirds  of  a  stick  of  silica-free  potassium 
hydroxide,  adding,  if  there  be  much  sulphur  present, 
a  little  potassium  nitrate  (in  the  case  of  heavy  sul- 
phides add  quite  a  little' nitre)  and  allow  to  cool. 
When  cold  weigh  out  -J  gram  of  the  material  to 
be  analyzed  and  brush  it  into  the  crucible.  Place  the 
cover  in  place  and  fuse,  beginning  with  a  very  low 
heat.  Be  very  careful,  if  you  are  working  on  a  sul- 
phide, to  raise  the  heat  very  gently  at  first,  as  the  union 
of  the  sulphur  and  nitre  takes  place  very  violently. 
After  the  mass  in  the  crucible  has  become  quiet  raise 
the  heat  and  heat  for  about  15  minutes.  Have  a 


28       MILL   AND    SMELTER   METHODS. 

large  casserole  heated  nearly  to  the  temperature  of 
the  stove.  When  the  fusion  is  ready  remove  the 
casserole  to  the  table  and  pour  the  contents  of  the 
crucible  into  it.  Set  the  crucible  in  also,  upright. 
When  quite  cold  rinse  out  with  hot  water ;  finally,  fill 
the  crucible  with  strong  hydrochloric  acid,  upset  it 
and  roll  around  in  the  solution  a  few  times,  rinse  off 
and  remove.  Evaporate  to  dryness.  Take  up  in 
hydrochloric  acid  and  water,  boil  and  filter  Wash 
once  or  twice  with  hot  I  to  i  hydrochloric  acid  and 
water,  then  several  times  with  hot  water.  Burn  and 
weigh. 

If  the  silica  is  black  after  burning,  some  silver 
chloride  has  been  left  in  the  silica  and  has  been  reduced 
to  metallic  silver  in  the  muffle ;  but,,  if  the  washing 
with  hot  dilute  hydrochloric  is  thorough  this  will  not 
occur. 

Silica,  Iron  and  Lime 

In  ores  these  three  elements  are  generally  deter- 
mined on  the  one  weighing.  To  £  gram  of  the  ore 
add  15  cc.  of  hydrochloric  acid  and  10  ce.  of  nitric 
acid  and  evaporate  to  dryness  in  a  beaker.  Take  up 
in  10  cc.  of  hydrochloric  acid  and  20  cc.  of  water,  boil 
and  filter.  Burn  and  weigh  the  insoluble  residue, 
which,  in  smelter  parlance,  is  called  the  silica.  To  the 
filtrate  add  ammonia  to  precipitate  the  iron,  boil  a 
few  minutes  and  filter.  To  the  filtrate  add  ammonium 
oxalate,  boil  and  filter  off  the  calcium  oxalate. 

The  iron  on  the  filter  paper  is  dissolved  with  hy- 


MILL   AND    SMELTER    METHODS.       29 

drochloric  acid,  warmed,  reduced  with  stannous  chlo- 
ride, cooled,  titrated  with  potassium  bichromate. 

The  calcium  oxalate  is  proceeded  with  as  in  lime 
in  slags. 

In  the  case  of  copper  ores,  where  there  is  no  lime 
present,  the  hydrochloric  acid  solution  of  the  iron  may 
be  reduced  with  test  lead ;  the  copper  will  not  then  in- 
terfere with  the  bichromate  titration. 

If  the  ore  is  a  sulphide,  the  first  evaporation  to 
dryness  should  be  made  with  15  cc.  of  the  "chlorate 
mixture." 

Zinc. 

Zinc  in  an  ore  is  treated  essentially  as  in  slags,  by 
a  modification  of  Low's  method.  Cadmium  may  be 
removed  when  necessary  by  passing  hydrogen  sul- 
phide through  the  acid  solution  before  adding  the  test 
lead.  CdS  and  CuS  are  then  precipitated  together 
and  must  be  filtered  out.  The  addition  of  test  lead 
is  then  unnecessary.  The  hydrogen  sulphide  will  not 
interfere. 

Manganese. 

Essentially  as  in  slags.     Often,  however,  it  is  only 
necessary  to  boil  the  ore  with  hydrochloric  acid. 
Sulphur. 

To  I  gram  of  ore  add  10  cc.  of  chlorate  mixture 
and  evaporate  to  dryness.  Take  up  in  10  cc.  hydro- 
chloric acid  and  10  cc.  water  and  boil.  Now  add  20  cc. 
of  ammonia  and  5  cc.  of  hydrogen  peroxide  and  fil- 
ter (the  lead,  iron,  etc.,  will  be  on  the  filter  paper). 


30       MILL   AND    SMELTER    METHODS. 

Boil  the  filtrate  after  making  it  acid  with  hydro- 
chloric acid,  then  add  -J  gram  of  a  solution  of  barium 
chloride.  Allow  to  settle,  filter,  wash  well  with  water, 
burn  in  the  muffle  and  weigh  as  barium  sulphate.  The 
weight  times  .13734  gives  the  per  cent  of  sulphur. 
Copper  and  Lead. 

To  i  gram  of  ore  add  15  cc.  of  hydrochloric  acid 
and  boil  for  a  few  minutes.  Now  add  15  cc.  of  nitric 
acid  and  10  cc.  of  sulphuric  acid  and  evaporate  to 
dense  white  fumes  of  SO3.  Cool,  add  30  cc.  of  cold 
water  and  filter. 

Place  in  the  filtrate  a  small  piece  of  aluminum 
foil  (ij  inches  square  and  with  the  diagonal  corners 
bent  in  opposite  directions)  and  boil  until  all  the  cop- 
per is  precipitated  on  the  aluminum.  Filter  and  test 
the  filtrate  for  copper  with  hydrogen  sulphide.  Dis- 
solve the  copper  in  as  little  nitric  acid  as  possible, 
add  a  few  drops  of  water  and  evaporate  to  about  5  cc. 
Cool,  add  20  cc.  of  water  and  5  cc.  of  ammonia,  boil 
three  to  four  minutes,  add  5  cc.  of  acetic  acid,  cool 
and  titrate  with  the  sodium  thiosulphate  solution.  Be- 
fore proceeding  to  titrate,  add  3  grams  of  potassium 
iodide  crystals  and  shake  well.  Add  a  few  drops  of 
the  starch  solution  after  the  yellow  color  has  begun 
to  fade.  (See  standardizing  the  solution.) 

Now  take  the  filter  paper  containing  the  lead  sul- 
phate, place  it  in  a  beaker  with  10  grams  of  ammonium 
acetate  and  50  cc.  of  hot  water.  Heat  until  all  the 
sulphate  is  dissolved.  Remove  from  the  heat. 


MILL   AND    SMELTER    METHODS.       31 

add  a  few  drops  of  acetic  acid  and  titrate  with  the 
ammonium  molybdate  solution,  using  the  tannic  acid 
indicator. 

Baryta. 

The  insoluble  residue  from  the  acid  treatment  is 
fused  with  alkaline  carbonates,  dissolved  in  hot  water, 
the  precipitate  of  barium  carbonate  filtered  out,  dis- 
solved in  dilute  hydrochloric  acid,  boiled,  the  barium 
precipitated  as  barium  sulphate  by  means  of  sulphuric 
acid.  Or,  the  weight  of  the  residue  in  the  platinum 
crucible  being  known,  add  a  few  drops  of  sulphuric 
acid  and  a  few  drops  of  hydrofluoric  acid,  place  on 
the  hot  plate  and  evaporate  to  dryness.  Weigh ;  the 
difference  between  the  two  weights  will  be  the  true 
silica. 

Antimony  and  Arsenic. 

In  ores,  mattes  or  speiss,  flue  dust,  dross,  etc.  To 
i  gram  of  ore  in  a  3-inch  casserole  add  10  cc.  nitric 
acid  and  warm.  After  the  evolution  of  red  fumes 
has  nearly  ceased,  add  about  10  cc.  of  sulphuric  acid 
and  run  down  to  copious  fumes  of  sulphuric  acid.  Do 
not  boil  too  long  after  the  dense  white  fumes  of  sul- 
phuric acid  have  started,  or  some  small  amounts  of 
arsenic  may  be  volatilized. 

Allow  the  casserole  to  cool  and  add  40  cc.  of  cold 
water  and  10  cc.  of  hydrochloric  acid.  Some  tartaric 
acid  should  be  added  also  if  antimony  is  to  be  deter- 
mined. Boil  to  dissolve  all  soluble  matter.  If  much 
gangue  is  present,  filter;  if  not,  wash  into  a  No.  3 


32       MILL   AND    SMELTER   METHODS. 

Griffin  lipped  beaker,  using  warm  water,  and  reduce 
to  a  colorless  solution  \vith  a  mixture  of  one  part  of 
ammonium  bi-sulphite  and  two  parts  of  strong  am- 
monia. The  reduction  is  best  made  by  adding  the  am- 
moniacal  solution  drop  by  drop  with  constant  stirring, 
waiting  for  the  precipitate  formed  to  dissolve  after 
each  addition.  Do  not  add  any  more  sulphite  than 
that  necessary  to  reduce  to  the  colorless  stage.  Add 
a  little  more  hydrochloric  acid  in  case  all  the  hydrates 
formed  do  not  dissolve.  If  there  is  much  gold,  sele- 
nium or  tellurium  in  the  ore,  these  metals  will  be  pre- 
cipitated by  the  excess  of  sulphurous  acid  and  darken 
the  solution;  so,  if,  after  the  solution  is  nearly  color- 
less, this  darkening  occurs,  no  more  sulphite  need  be 
added. 

Boil  the  solution  a  few  minutes  until  there  is  no 
apparent  odor  of  sulphurous  acid,  and  then  while  still 
warm,  pass  in  a  lively  current  of  hydrogen  sulphide 
gas  for  about  fifteen  minutes,  or  until  the  precipitate 
gathers  together  and  the  super-natant  liquid  does  not 
appear  murky.  It  is  safer  to  pass  the  gas  through  for 
a  longer  time,  but  in  case  of  hurry,  after  some  expe- 
rience, the  point  may  be  told  almost  with  certainty  by 
inspection. 

Filter  the  precipitated  sulphides  through  an  n 
cm.  filter  paper  and  wash  the  sulphides  all  onto  the 
paper  with  water.  Wash  out  the  iron  salts.  Test  the 
filtrate  with  hydrogen  sulphide  gas. 

Put    the    paper    containing    the  sulphides    into    a 


MILL   AND    SMELTER    METHODS.       33 

4-ounee  distillation  flask,  the  arm  from  the  neck  of 
which  is  bent  down  at  the  end  so  as  to  connect  with 
a  12-inch  Liebig  condenser  set  vertically.  If  the,  sul- 
phides are  too  bulky  to  wrap  in  the  paper  and  put 
into  the  flask,  pierce  the  filter  and  wash  most  of  the 
precipitates  through  the  funnel  into  the  flask,  using  a 
minimum  wash  of  a  volume  of  hydrochloric  acid  and 
i  volume  of  water,  used  in  a  wash  bottle  with  a  Bun- 
sen  valve. 

Remove  the  paper  and  put  it  into  the  flask,  then 
pour  through  the  funnel  to  wash  it  50  cc.  of  the  cupric 
chloride  solution.  Always  pour  the  chloride  solution 
in  through  a  funnel  reaching  below  the  opening  at  the 
side  of  the  neck,  so  as  to  avoid  getting  copper  into  the 
distillate. 

A  thermometer  through  a  rubber  stopper  is  in- 
serted in  the  neck  of  the  flask,  reaching  to  within 
about  jr  inch  from  the  bottom.  The  flask  is  set  on  a 
sand  bath  4  inches  in  diameter,  so  that  .the  naked 
flame  shall  not  play  on  the  sides  of  the  flask,  thus 
avoiding  the  raising  of  the  temperature  at  any  spot, 
above  that  desired.  Allow  the  outlet  of  the  condenser 
to  dip  about  J  an  inch  into  a  beaker  of  cold  water. 

Heat  the  flask  gradually  until  the  thermometer 
reads  115  degrees  centigrade,  then  remove  the  stopper 
and  add  10  to  25  cc.  of  strong  hydrochloric  acid,  col- 
lecting the  second  distillate  in  water  as  before. 

The  distillate  is  poured  into  a  No.  3  beaker,  made 
alkaline  with  ammonia,  just  acidified  with  hydro- 


34       MILL   AND    SMELTER    METHODS. 

chloric  acid,  cooled,  about  8  grams  of  bicarbonate  of 
soda  and  some  starch  solution  added,  and  titrated 
with  the  standard  iodine  solution. 

Antimony  may  now  be  determined  after  removing 
the  stopper  containing  the  thermometer  and  inserting 
another  through  which  is  a  glass  tube  reaching  nearly 
to  the  bottom  of  the  flask  and  connected  to  a  hydro- 
chloric acid  generator.  This  generator  contains  hy- 
drochloric acid  into  which  sulphuric  acid  is  allowed  to 
drop  from  a  separatory  funnel  at  the  rate  of  about 
two  drops  per  second.  The  condenser  is  sealed  with 
cold  water  as  for  the  arsenic  distillation  and  heat  is 
applied  to  the  flask  until  the  contents  become  about 
dry.  Do  not  heat  to  a  much  higher  point,  since  cop- 
per chloride  is  liable  to  come  over.  Remove  the 
beaker  containing  the  distillate,  add  a  little  tartaric 
acid,  almost  neutralize  with  ammonia  and  pass  in  hy- 
drogen sulphide  gas.  If  the  orange  antimony  sul- 
phide shows  up,  put  under  the  condenser  other  beak- 
ers of  water  as  seals,  keeping  up  the  heating  and  pass- 
ing in  of  the  hydrochloric  acid  gas  until  no  precipi- 
tate is  formed  with  hydrogen  sulphide. 

Filter  the  sulphide  of  antimony  into  a  tarred 
Gooch  crucible,  heat  in  an  air  bath  at  255  degrees  C. 
for  one  hour,  and  weigh.  The  weight  multiplied  by 
71.40  will  give  the  amount  of  antimony. 

It  takes  about  fifteen  minutes  each  for  the  arsenic 
and  antimony  distillations.  In  the  distillation  some 
uncombined  sulphur  comes  over,  but  does  not  affect 


MILL   AND    SMELTER    METHODS.       35 

the  results.  No  sulphurous  acid  or  hydrogen  sulphide 
will  be  found  with  the  arsenous  chloride  distillate. 
Antimoriious  chloride  can  not  be  titrated,  owing  to 
other  decompositions  from  the  high  temperatures  re- 
quired to  distill  it. 

The  solutions  required  are :  Cupric  chloride  ;  dis- 
solve 300  grams  of  pure  cupric  chloride  crystals  in  I 
litre  of  hydrochloric  acid.  This  solution  is  mixed  with 
i  litre  of  a  solution  of  zinc  chloride,  which  boils  at 
180  degrees  C.  The  zinc  chloride  may  be  made  by 
adding  successively  to  i  pound  of  pure  stick  zinc  500 
cc.  of  water  and  1,250  cc.  of  hydrochloric  acid.  After 
the  zinc  is  in  solution,  bring  to  a  boil  and  evaporate 
a  little  to  bring  the  boiling  point  up  to  180  degrees  C., 
this  making  about  1,100  cc.  of  solution. 


Standard    Iodine    Solution. 


This  is  best  made  so  that  i  cc.  equals  .00$  grams 
of  arsenic.  Dissolve  about  40  grams  of  potassium 
iodide  in  a  minimum  of  water,  and  to  this  add  17 
grams  of  iodine.  After  the  iodine  is  all  dissolved, 
make  up  to  i  litre  with  distilled  water. 

To  standardize,  dissolve  .300  mgs.  of  C.  P.  arse- 
nious  acid  in  a  little  caustic  soda  or  potash,  dilute  to 
about  .200  cc.,  acidify  slightly  with  hydrochloric  acid, 
add  about  2  grams  of  sodium  bicarbonate,  some  starch 
solution  and  titrate  to  a  permanent  blue.  The  arse- 
nious  acid  contains  75.76%  of  arsenic. 


36       MILL   AND    SMELTER    METHODS. 

This  method  is  due  to  Messrs.  Lewis  B.  Skinner 
and  R.  H.  Hawley  of  Colorado  Springs,  Colorado. 

Modification. 

Treat  the  ore  with  nitric  acid,  and  when  violent 
action  ceases,  add  5  to  10  cc.  of  hydrochloric  acid  and 
evaporate  to  dryness.  If  the  sample  contains  organic 
matter,  as  in  the  case  of  flue  dust,  treat  with  nitric 
acid  and  potassium  chlorate.  Take  up  in  water  and 
hydrochloric  acid,  filter  off  the  residue,  neutralize 
with  ammonia,  make  acid  with  hydrochloric  acid  to 
re-dissolve  the  precipitate,  then  add  some  sodium  sul- 
phide solution  and  heat  to  drive  off  the  excess  of  sul- 
phur dioxide.  Precipiate  with  hydrogen  sulphide 
solution  and  proceed  as  before. 


Mixture    Beds. 


Smelter  ore  beds  vary  in  size  from  1,000  tons  to 
several  thousand  tons,  and  are  built  up  of  the  daily 
ore  supplies  that  reach  the  works.  This  ore  is  spread 
out  in  layers,  so  as  to  have  as  even  a  mixture  as  pos- 
sible. When  a  given  bed  is  about  completed,  it  be- 
comes necessary  to  determine  its  exact  chemical  com- 
position, so  that  the  last  layer  can  be  added  of  ores 
of  such  nature  as  to  bring  the  whole  up  to  the  definite 
composition  required  for  the  smelter  charges,  or  the 
metallurgist  can,  if  he  so  desires,  add  the  necessary  in- 
gredients to  each  charge.  When  this  is  done  the  fur- 
naces are  run  continuously  on  the  given  bed,  receiving, 


MILL   AND    SMELTER    METHODS.       37 

of  course,  ore  of  uniform  composition  and  obtaining 
uniform  metallurgical  results. 

In  order  to  analyze  an  ore  bed,  the  chemist  makes 
up  a  miniature  ore  bed  from  the  samples  of  the  ores 
that  formed  that  particular  bed.  He  is  given  such  a 
list  as  the  following : 

Weight  of  Ore  Sample 

Mine —                                  in  Pounds.  Number. 

Portland 243,342  820 

Summit 23,800  560 

Hercules 44,160  900 

The  chemist  has  already  analyzed  these  ores  and 
still  has  the  samples.  From  these  he  now  makes  up 
a  miniature  bed,  substituting  grams  for  thousand 
pounds.  Hence,  on  Summit  No.  560,  above,  he  would 
weight  out  23.8  grams,  and  so  on.  Since  the  beds  aver- 
age over  1,000  tons,  he  will  have  a  very  large  sample, 
which  he  will  mix  thoroughly  and  quarter  down  to  a 
sample  of  about  J  pound.  From  this  he  will  make 
his  analysis,  saving  the  remainder  of  the  sample  in 
case  it  should  be  necessary  to  repeat  the  determina- 
tion. 

On  all  beds  the  following  are  determined:  Total 
insoluble,,  true  silica,  iron,  lime,  manganese,  baryta 
and  sulphur;  sometimes  zinc,  alumina,  lead  (when  not 
determined  by  fire  assay),  copper  and  other  elements 
may  be  called  for. 

Silica,  iron,  lime,  manganese,  copper  and  lead  are 


38       MILL   AND    SMELTER    METHODS. 

determined  by  any  of  the  mtehods  already  given  un- 
der "Ores." 

Alumina,  Etc. 

A  hydrochloric  acid  solution  of  the  soluble  portion 
of  the  ore  is  obtained,  the  insoluble  residue  ignited  and 
weighed  in  a  platinum  crucible,  fused  with  alkaline 
carbonates,  extracted  with  water  and  HC1,  evapo- 
rated to  dryness  to  separate  the  silica.  Then  proceed 
as  in  slags,  after  adding  the  portion  soluble  in  acid 
.above,  and  from  which  the  copper  has  been  removed. 


Briquettes. 


When  flue  dust,  fine  ore  and  sweepings  are  to  be 
used  in  the  blast  furnace,  the  customary  method  is  to 
briquette  the  material  first.  Such  briquettes  will  con- 
tain all  sorts  of  material,  but  the  customary  analyses 
call  for  silica,  iron,  lime,  lead,  copper,  sulphur  and 
zinc. 

Silica  and  Iron. 

Place  about  2  grams  of  the  sample  in  an  agate 
mortar  and  crush  as  finely  as  possible  (this  is  made 
necessary  by  the  fact  that  fine  coke  is  often  disposed 
of  in  the  briquettes).  From  this  pulverized  portion 
weigh  -J  gram  into  a  small  evaporating  dish,  add  10 
cc.  of  chlorate  mixture  and  evaporate  to  dryness. 
Remove  and  cool  the  dish  and  then  run  to  dryness 
once  more  with  10  cc.  of  HC1.  Take  up  in  HC1  and 
water,  filter  out  the  insoluble  residue  and  burn  it  in 


MILL   AND    SMELTER    METHODS.       39 

the  muffle.  Now  place  the  insoluble  residue  in  a  sil- 
ver crucible  and  fuse  it  with  the  smallest  possible 
amount  of  KOH.  Dissolve  in  hot  water,  add  5  cc.  of 
HC1  and  evaporate  to  dryness  in  a  casserole ;  take  up 
in  water  and  HC1  as  before,  filter  off  the  silica,  burn 
and  weigh. 

The  filtrate  from  the  insoluble  residue  and  that 
from  the  silica  are  now  combined,  boiled,  reduced 
with  stannous  chloride  and  titrated  with  potassium 
bichromate. 

Lime. 

Since  the  lime  is  usually  added  to  the  "bricks" 
in  the  form  of  slaked  lime,  it  is  easily  soluble  in  dilute 
HC1.  To  one  gram  of  the  sample,  add  from  10  to  15 
cc.  of  dilute  HC1  and  bring  to  a  boil.  Precipitate  the 
iron  with  ammonia  and  add  3  cc.  of  hydrogen  perox- 
ide to  hold  up  the  lead.  Boil  and  filter.  Heat  the 
filtrate  to  boiling  and  precipitate  the  lime  with  am- 
monium oxalate.  Filter  and  wash  thoroughly  with 
hot  water.  Proceed  as  in  lime  in  "Slags." 

Zinc,  copper,  lead  and  sulphur  are  determined  as 
in  any  of  the  methods  already  given. 

Note. — Fine  grinding  is  only  necessary  for  the 
portion  on  which  the  silica  is  to  be  determined;  the 
ordinary  sample  room  fineness  of  100  mesh  is  suffi- 
'ient  for  all  the  other  determinations. 


40       MILL   AND    SMELTER    METHODS. 


CHAPTER   IV. 


Coal  and   Coke. 


Proximate   Analyses    (Heinrichs). 

Weigh  out  in  duplicate  I  gram  of  powdered  coal ; 
place  in  a  small  beaker,  cover  with  a  watch  glass  and 
place  on  the  steam  dryer  for  twenty-four  hours.  Take 
off  and  weigh ;  the  loss  found  multiplied  by  100  equals 
the  percentage  of  moisture  in  the  coal. 

Weigh  i  gram  of  the  powdered  coal  into  a  medium 
sized  porcelain  crucible,  put  the  cover  on  and  place 
the  crucible  in  a  medium  hot  muffle  and  allow  it  to 
remain  until  fumes  cease  to  come  out  around  the 
edge  of  the  cover.  Remove,  cool  and  weigh ;  the  loss 
less  the  moisture  previously  found,  multiplied  by  100, 
equals  the  percentage  of  volatile  combustible  matter. 
This  should  also  be  done  in  duplicate  and  the  results 
should  check. 

After  weighing  the  volatile  matter,  put  the  mate- 
rial back  in  the  crucible,  replace  the  cover  and  return 
to  the  muffle  until  the  ash  turns  white,  showing  the 
carbon  to  be  completely  burned  off.  Remove,  cool 
and  weigh.  The  difference  between  this  weight  and 
the  last,  multiplied  by  100,  equals  the  percentage  of 
fixed  carbon ;  the  remainder  is  ash,  which,  multiplied 
by  100,  equals  the  percentage  of  ash. 


MILL   AND    SMELTER    METHODS.       41 

Coke. 

Essentially  the  same  method  as  for  coal.  Coke 
ash  is,  however,  analyzed  for  silica,  iron,  alumina  and 
lime,  as  follows :  Burn  about  5  grams  of  coke  in  the 
muffle  in  order  to  have  sufficient  ash.  Pulverize 
about  2  grams  finely  in  an  agate  mortar  and  from  this 
weigh  out  and  fuse  in  a  platinum  crucible  £  gram 
with  from  5  to  7  grams  of  mixed  alkaline  carbonates. 
Dissolve  in  water  and  hydrochloric  acid  and  run  to 
dryness,  take  up  with  hydrochloric  and  nitric  acids 
and  filter  off  the  silica,  burn  and  weigh.  The  filtrate 
is  neutralized  and  boiled  with  caustic  potash.  The 
iron  is  filtered  off,  dissolved  in  hydrochloric  acid,  re- 
duced with  stannous  chloride  and  titrated  with  po- 
tassium bichromate. 

To  the  filtrate  from  the  iron  add  hydrochloric  acid 
in  very  slight  excess,  neutralize  with  ammonia,  boil, 
filter  and  burn  the  precipitate  and  weigh  as  A12O3. 

On  the  filtrate  from  the  alumina,  made  alkaline 
with  ammonia,  lime  is  determined  by  means  of  ammo- 
nium oxalate. 

Magnesium,  when  called  for,  may  be  determined 
essentially  as  in  the  method  given  under  magnesium 
in  slags. 


42       MILL   AND    SMELTER    METHODS. 


CHAPTER  V. 


Other   Methods   of  Analysis, 


The   methods   mentioned   previously   are   those   in 
general   use.     There  remain,  however,  other   methods 
designed  to  meet  exceptional  cases,  etc.,  and  methods 
that  may  be  used  as  checks  on  those  already  given. 
Antimony  and  Arsenic. 

To  I  gram  of  material  add  dilute  nitric  acid  (50%) 
and  evaporate  almost  to  dry  ness ;  take  up  in  5  to  10 
cc.  HC1  and  boil.  Add  an  excess  of  sodium  sulphide 
and  boil  well.  (In  the  presence  of  copper  avoid  am- 
monium sulphide.)  Filter  and  retreat  the  black  sul- 
phides. Now  combine  the  filtrates,  acidify  with  HC1, 
boil  and  filter  (avoid  an  excess  of  HC1).  Wash  the 
sulphides  off  the  filter  with  water,  add  potassium  chlo- 
rate and  boil  until  free  chlorine  ceases  to  come  off. 
Cool,  make  strongly  alkaline  with  ammonia,  add  mag- 
nesium chloride  (in  case  very  little  arsenic  is  pres- 
ent, let  stand  five  to  six  hours,  agitating),  filter  and 
wash  with  strong  ammonia.  Dissolve  the  magnesium 
arsenate  in  50%  HC1,  add  potassium  iodide  and  let 
stand  because  the  action  is  slow.  Titrate  with  the 
thio-sulphate  solution  as  in  copper. 

Acidify  the  filtrate  from  the  magnesium  arsenate 


MILL   AND    SMELTER    METHODS.       43 

with  HC1,  then  lead  in  hydrogen  sulphide  gas,  warm 
and  filter.  Dissolve  the  precipitated  antimony  sul- 
phide in  KOH,  wash  into  a  flask,  washing  the  filter 
paper  with  HC1  containing  a  little  potassium  chlo- 
rate. Now  add  in  the  flask  a  little  more  chlorate  and 
boil  until  no  chlorine  is  apparent  on  iodide  starch 
paper  (be  careful  at  this  stage  not  to  volatilize  the 
antimony),  cool,  add  potassium  iodide  and  2  cc.  of 
carbon  di-sulphide  and  titrate  with  the  thio-sulphate 
solution. 

When  tin  is  present,  run  down  with  50%  HC1,  but 
avoid  dryness.  Add  yellow  potassium  sulphide,  or 
sodium  sulphide,  and  boil  well  for  an  hour.  Filter, 
(Sb  and  Sn  are  in  the  filtrate.  Volumetrically  tin 
does  not  interfere  with  As  and  Sb.)  Acidify  with 
H'Cl,  warm  and  filter.  Wash  the  precipitate  into  a 
beaker,  rinse  the  filter  paper  with  a  hot  concentrated 
solution  of  oxalic  acid  (in  which  stannic  sulphides  are 
soluble),  boil  and  filter.  Add  nitric  acid,  boil  until 
red  fumes  cease  (oxalic  acid  goes  to  carbonic  acid), 
evaporate  to  dryness,  take  up  in  yellow  ammoniiim 
sulphide,  re-precipitate  with  HC1,  filter  into  a  Gooch 
crucible  and  ignite  in  the  muffle.  Weigh  as  SnCX. 

Note. — There  are  three  ways  of  getting  rid  of 
oxalic  acid  in  the  above — by  permanganate  of  potas- 
sium, by  sulphuric  acid,  by  nitric  acid.  The  latter  is 
to  be  preferred,  because  nitric  acid  is  a  volatile  acid 
and  can  be  evaporated. 


44       MILL   AND    SMELTER    METHODS. 

Pattinsons  Method  (Modified). 

Weigh  into  a  No.  4  casserole  ^  gram  of  ore,  treat 
with  HNO3  and  HC1,  according  to  requirements,  i.  e., 
if  an  oxidized  ore,  little  or  no  nitric  acid  will  be  re- 
quired ;  if  a  sulphide,  from  5  to  8  cc,  will  be  required. 
Evaporate  to  dryness,  dissolve  in  15  cc.  strong  HC1, 
dilute  with  100  cc.  boiling  water,  add  an  emulsion  of 
oxide  of  zinc  until  the  solution  turns  red,  then  a  slight 
excess;  now  add  from  20  to  50  cc.  strong  bromine 
water,  according  to  the  amount  of  manganese  present, 
50  cc.  being  sufficient  to  ppt.  about  40%  Mn,  boil  until 
all  the  excess  Br  has  been  expelled,  and  filter  through 
a  large  filter,  washing  by  decantation,  until  free  from 
chlorides  and  bromides.  Remove  the  filter  and  its 
contents  carefully  from  the  funnel,  open  it  against 
the  side  of  a  No.  3  beaker,  wash  the  ppt.  into  the 
beaker  with  boiling  water,  cleaning  the  filter  paper 
as  thoroughly  as  possible. 

Fill  a  burette  with  a  volumetric  solution  of  oxalic 
acid  (see  table  on  page  i)  ;  from  this  burette  run  into 
the  casserole  10  cc.  of  the  solution,  add  20  cc.  dilute 
sulphuric  acid  ( i  to  i )  and  a  little  boiling  water.  Dis- 
solve all  the  MnO2,  etc.,  adhering  to  the  casserole  with 
this  mixture,  and  then  pour  it  over  the  filter  in  the 
beaker,  to  remove  what  still  sticks  to  it ;  wash  the 
filter  with  boiling  water  and  remove  it  from  the 
beaker.  Now  add  to  the  mixture  in  the  beaker  about 
30  cc.  more  of  the  oxalic  acid  solution  (an  excess  is 
required),  and  200  cc.  boiling  water.  If  everything 


MILL   AND    SMELTER    METHODS.       45 

does  not  dissolve,  heat  until  it  does  and  the  solution 
becomes  clear.  Titrate  with  the  volumetric  solution 
of  potassium  permanganate  until  just  pink. 

Now  determine  the  value  of  the  oxalic  acid  solution 
in  terms  of  the  permanganate  solution,  as  follows : 
Into  a  No.  3  beaker  run  40  cc.  oxalic  acid  solution,  add 
200  cc.  boiling  water,  then  20  cc.  dilute  sulphuric 
acid  (i  to  i),  and  titrate  with  the  permanaganate  (it  is 
best  to  make  the  solutions  exactly  equal  in  value  so 
that  i  cc.  equals  I  cc).  Divide  the  amount  of  perman- 
ganate solution  into  the  amount  of  oxalic  acid  solution, 
to  find  its  value  in  terms  of  oxalic  acid,  multiply 
the  number  of  cc.'s  of  permanaganate  solution  used  in 
the  titration  by  this  factor,  and  subtract  from  the 
amount  of  oxalic  acid  solution  used — in  the  above 
case  40  cc.'s — this  will  give  the  amount  of  oxalic  acid 
oxidized  by  the  MnO2,  obtained  from  the  ore. 

We  have  previously  found  (standardizing  a  solu- 
tion of  potassium  permanaganate)  that  the  ratio  of  iron 
to  oxalic  acid  is  as  8  to  9.  Hence, 

1.  Standardize  the  oxalic  acid  solution  with  the 
permanganate  solution  and  find  its  equivalent  in  Fe. 
Thus,  if  i  cc.  equals  i  cc.  exactly,  then  i  cc.  oxalic 
acid  equals  .01  Fe,  or,  if  I  cc.  oxalic  acid  equals  .9  cc. 
permanganate  solution,  then  i  cc.  oxalic  acid  solution 
equals  -.009  grams  Fe,  etc. 

2.  Multiply   the   equivalent   in   iron  by    1.125   to 
find  the  value  per  cc.  in  oxalic  acid,  i.  e.,  to  find  ex- 
actly how  much  H2C2O4,  2H2O,   i   cc.  of  the  oxalic 


46       MILL   AND    SMELTER    METHODS. 

acid  solution  contains.     This  amount  is  then  marked 
on  the  bottle. 

3.  Multiply  the  amount  of  oxalic  acid  oxidized 
by  the  MnO2  of  the  ore  by  .4365  to  find  the  equivalent 
in  Mn,  then  calculate  the  per  cent. ;  or  the  last  two 
may  be  combined  and  the  value  in  iron  multiplied  by 
(1.125x4365)  equals  .49106. 
Slags. 

Slags  which  will  not  decompose  by  treatment  with 
acids  may  be  either  sintered  or  fused. 

The  sintering  is  performed  (see  Furman's  Man- 
ual) in  a  small  platinum  dish  by  mixing  -J  gram  of 
the  slag  with  about  ij  (one  and  one-half)  grams 
sodium  carbonate  in  a  small  agate  mortar;  transfer 
this  to  the  platinum  dish,  brushing  the  mixture  to  a 
small  heap  in  the  center ;  now  place  in  the  muffle  and 
heat  until  the  mass  sinters  together.  Fusion  must 
not  take  place,  since  the  lead  would  be  reduced  and 
spoil  the  platinum  dish.  Remove  from  the  muffle, 
cool  by  dipping  the  bottom  of  the  dish  in  cold  water, 
then  add  2  cc.  water  and  5  cc.  HC1,  and  proceed  as 
previously  directed  under  silica. 

Fusion,  when  necessary,  is  conducted  as  follows : 
One-half  gram  of  slag  is  mixed  with  about  three 
times  as  much  fusion  mixture,  and  -J  gram  of  potas- 
sium nitrate  (this  is  added  to  keep  the  lead  from  re- 
ducing and  spoiling  the  crucible)  and  fuse  in  a  plat- 
inum crucible  in  the  muffle.  Cool  the  crucible  and 
place  in  a  No.  4  casserole  with  about  50  cc.  boiling 


MILL   AND    SMELTER    METHODS.       47 

water;  boil  until  clean,  take  out  crucible,  rinse  with 
hot  water,  using  finger  cot  if  necessary,  boil  until  dis- 
solved. Cover  with  a  watch  glass  and  add  through  a 
pipette  10  cc.  strong  HC1 ;  wash  off  the  cover,  remove 
it,  and  evaporate  to  dryness.  Treat  the  dry  mass 
with  50  cc.  dilute  HC1,  boil,  dilute  with  50  cc.  water, 
filter,  wash,  ignite  and  weigh  silica. 

Iron. 

To  the  filtrate  add  ammonia  in  slight  excess  to 
ppt.  the  iron,  filter  and  wash,  dissolve  the  ppt.  in 
dilute  HC1  and  proceed  in  the  usual  way. 

Lime. 

To  the  filtrate  from  the  iron  add  10  cc.  of  a  10% 
solution  of  oxalic  acid,  then  make  slightly  alkaine 
with  ammonia,  boil,  allow  to  settle,  filter,  wash,  pro- 
ceed in  the  usual  manner. 

Lead. 

The  purchase  and  sale  of  lead  ores  is  at  present 
based  on  the  fire  assay.  This  method,  though  inaccu- 
rate, appears  to  meet  the  commercial  requirements.* 
The  titration  by  ammonium  molybdate  already  given 
is  the  method  irf  general  use  where  lead  is  determined 
in  the  wet  way,  but  another  way,  by  titration  with 
potassium  permanganate,  is  also  in  use. 

In  this  method  the  lead  is  separated  first  as  metal, 


*  The  Colorado  Scientific  Society  is  at  present  gather- 
ing information  as  to  the  best  method  of  determining  lead 
in  ores  of  varying  composition. 


48       MILL   AND    SMELTER    METHODS. 

then  dissolved  and  pptd.  as  oxalate,  the  acid  oxalate 
being  titrated  with  permanganate  of  potassium. 

Treat  -J  gram  of  ore  with  15  cc.  strong  nitric  and 
10  cc.  strong  sulphuric  acids,  and  evaporate  to  white 
fumes  over  a  strong  heat,  cool,  add  50  cc.  cold  water 
and  2  grams  of  Rochelle  salts,  boil,  filter,  wash  with 
dilute  sulphuric  acid  ( I  to  i ) ,  and  then  with  water. 

Wash  the  lead  sulphate  back  into  the  casserole, 
add  10  grams  ammonium  chloride,  25  cc.  water,  ana 
boil  until  dissolved;  filter  and  wash  with  a  little  more 
solution  of  ammonium  chloride,  wash  with  boiling 
water.  The  filtrate  should  be  received  in  a  No.  2 
beaker,  containing  the  Al  foil,  such  as  was  used  in 
the  Cu  determination.  Boil  five  minutes,  when  the 
lead  will  be  completely  pptd.,  and,  if  in  considerable 
quantity,  will  usually  separate  from  the  foil  and  unite 
into  a  spongy  mass.  Decant  the  solution  from  the 
lead  and  aluminum  into  the  casserole  and  fill  the 
beaker  with  boiling  water;  discard  the  solution  in  the 
casserole,  being  careful  that  no  lead  has  escaped.  Now 
remove  the  Al  foil  and,  with  the  finger  cot,  remove 
any  adhering  lead,  wash  the  foil  with  boiling  water, 
decanting  as  closely  as  possible  the  last  time.  Pour 
over  the  piece  of  Al  foil  6  cc.  dilute  nitric  acid,  to 
dissolve  any  particles  of  lead  adhering  to  it.  remove 
the  foil  with  a  glass  rod,  washing  it  slightly  with  a 
stream  of  water  from  the  wash  bottle,  heat  the  acid  in 
the  casserole  to  boiling  so  as  to  dissolve  the  particles 
of  lead,  then  pour  it  upon  the  greater  portion  of  lead 


MILL   AND   SMELTER   METHODS.       49 

in  the  beaker,  heat  until  dissolved,  add  a  few  drops 
of  an  acid  solution  of  phenolphthalein,  then  add  a  so- 
lution of  sodium  hydroxide  until  slightly  alkaline, 
then  10  cc.  of  a  solution  of  oxalic  acid  (i  in  10),  cool, 
filter,  wash  with  cold  water  several  times  until  excess 
of  oxalic  acid  is  removed.  Remove  the  filter  paper 
from  the  funnel,  open  against  the  side  of  a  No.  2 
beaker,  wash  the  ppt.  from  the  paper  into  the  beaker 
with  hot  water,  add"  5  cc.  dilute  sulphuric  acid  and 
titrate  with  a  solution  of  potassium  permanganate 
made  by  diluting  i  volume  of  the  i%  solution  with  4 
volumes  of  water,  making  a  solution  of  which  I  cc. 
equals  .002  Fe.  Multiply  the  value  of  the  solution  in 
Fe  by  1.85  to  obtain  its  value  in  Pb. 
Comparing  the  equations  : 

10  FeSO4  +  2  KMnO4  +  8  H2SO4  =•  5  Fe2(SO4)3 
+  K2SO4  +  2  MnSO4  +  8  H2O 
and 

10  FeSO4  +  2  KMnO4  +  8  H2SO4  =  5  Fe2(SO4)3 
+2  MnSO4+K2SO4+5  PbSO4+8  H2O 
We  see  that  the  same  amount  of  potassium  perman- 
ganate will  oxidize  five  equivalents  of  Pb  oxalate,  or 
ten    equivalents    of     ferrous    sulphate;     5x207,    the 
atomic  weight  of  lead,  therefore,  are    equivalent    to 
10x56,  the  atomic  weight  of  Fe.    From  this  we  obtain 
the  above  factor, 
5 


560 


50       MILL  AND   SMELTER   METHODS. 

Copper. 

Cyanide  Method. — Weigh  i  gram  into  an  8-ounce 
flask,  add  from  8  to  15  cc.  strong  nitric  acid  (accord- 
ing to  the  amount  of  sulphides  in  the  ore),  then  add 
5  cc.  strong  H2SO4  and  evaporate  to  white  fumes 
over  a  strong  heat,  eliminating  all  nitric  acid;  remove 
and  place  on  a  piece  of  asbestos  to  cool ;  when  cold, 
add  30  cc.  cold  water  and  6  grams  of  sheet  zinc  in 
strips ;  allow  to  stand  until  the  evolution  of  hydrogen 
has  nearly  ceased,  then  add  10  cc.  strong  commercial 
H,SO4  and  50  cc.  water,  mix  by  shaking  the  flask, 
and  allow  it  to  stand  until  the  zinc  has  completely 
dissolved,  all  action  has  ceased,  and  the  black  or  red 
ppt.  of  copper  has  completely  settled  to  the  bottom 
of  the  flask.  Fill  up  the  flask  with  hot  water,  shake, 
and  allow  to  settle  completely.  Carefully  decant  off 
as  much  of  the  liquid  as  possible,  leaving  all  the  ppt, 
in  the  flask ;  repeat  this  washing  three  times.  Dis- 
solve the  pptd.  Cu  in  5  cc.  strong  nitric  acid  and  boil 
off  the  red  fumes,  cool,  add  20  cc.  cold  water,  then 
10  cc.  strong  ammonia,  then  50  cc.  cold  water,  mix, 
titrate  with  the  volumetric  solution  of  KCN  until 
the  blue  color  has  become  faint,,  but  still  indicates  Cu. 
Filter  rapidly  through  a  20  cm.  Prat  Dumas  plaited 
filter  paper,  using  a  funnel  with  a  2-inch  stem,  wash 
with  a  little  water,  then  finish  the  titration  exactly 
as  in  standardizing  the  solution. 

Multiply  the  number  of  cc.  used  by  the  standard 


MILL   AND   SMELTER   METHODS.       51 

previously  found,  and  the  result  by  100,  gives  the 
percentage  Cu.* 

Or,  if  the  assay  of  the  ore  is  known  (since  2  Ag 
equals  I  Cu,  or  i%  Ag  equals  0.3%  Cu),  deduct  .1% 
Cu  for  each  100  ounces  Ag  present.  Zinc  and  nickel, 
which  interfere  with  the  titration  by  cyanide,  not 
being  pptd.  by  the  zinc,  have  been  removed.  Lead  has 
been  converted  into  insoluble  sulphate,  or  subse- 
quently that  derived  from  the  sheet  Zn  used,  has  been 
pptd.  as  hydrate  by  ammonia. 

In  both  the  iodide  method  (given  previously)  and 
in  this  method,  when  the  Cu  is  over  20%,  a  standard 
of  C.  P.  Cu.  should  be  run  at  the  same  time  as  the 
ore,  and  the  ore  should  be  run  in  duplicate,  and  the 
results  should  check. 


Colorimetric — To  Make  Up  the  Standard. 


One  gram.C.  P.  copper  foil  is  dissolved  in  just  as 
little  HNO3  as  possible,  then  10  cc.  more  of  HNO3  is 
added.  Thoroughly  boil  off  the  red  fumes,  and  add 
distilled  water  up  to  1000  cc.  From  this  solution 
i  cc.  is  used  for  every  1/10%.  Make  alkaline  with  20 
cc.  NH4OH,  and  add  enough  distilled  water  to  bring 
the  bulk  up  to  350  cc.  The  standards  are  placed  in 

*  Only  Ag  interfers  with  this  method;  it  can  be  re- 
moved by  adding-  a  few  drops  of  HC1  to  the  nitric  acid 
solution  of  the  copper  before  adding  the  ammonia;  shake 
well  to  make  the  silver  clot,  then  filter  into  another  flask 
and  wash  well  with  cold  water;  add  10  cc.  of  ammonia  and 
proceed  as  before. 


52       MILL   AND    SMELTER   METHODS. 

large  salt-mouth  bottles  of  colorless  glass,  with 
glass  stoppers.  These  are  kept  in  a  suitable  rack, 
which  is  lined  with  white  paper  and  placed  in  a  well 
lighted  part  of  the  room. 

Copper  in  Slags  and  Tailings. 

Weigh  2  grams  of  the  pulp  into  a  No.  2  beaker, 
add  5  cc.  HC1,  and  run  to  dryness  on  the  steam 
bath.  Take  up  with  5  cc.  HNO3  and  boil  until  copi- 
ous fumes  are  driven  off.  Now  add  distilled  water 
and  remove  from  the  plate.  Add  20  cc.  NH4OH,  and 
filter  into  glass  bottles.  Wash  twice  with  boiling  wa- 
ter, to  wash  any  salt  of  copper  out  of  the  precipitate. 
Fill  the  bottle  with  water  to  the  350  cc.  mark.  The 
bottle  is  then  compared  with  the  standards  and  the 
reading  divided  by  2. 

The  mill  tailings  run  higher  in  copper,  hence  use 
only  i  gram.  Add  5  cc  of  a  mixture  of  HNO3+KC1O3 
and  heat  for  1-5  minutes.  Now  add  30  cc.  water  and 
remove.  Proceed  as  before. 

Specimen    Lead   Slag   Analysis. 

% 

Si02 30.0 

FeO 28.7 

MnO 54 

CaO  14-2 

MgO 2.3 

ZnO  57 

A1203 5-6 


91.9 


MILL   AND    SMELTER    METHODS.       53 

Specimen    Bed  Analysis  for  Lead  Smelter. 

Total  Insoluble,  42.4%. 

% 

SiO2 33.2 

Fe 12.4 

Mn 4.0 

CaO  4-5 

BaSO4  9.2 

MgO 0.7 

Zn   2.2 

A12O8 6.0 

Pb 14.7 

Cu 0.3 

S   47 

Specimen    Briquette    Analysis. 

% 

SiO2  . . . . 15.0 

Fe   35.0 

Zn   2.2 

CaO 4.1 

Cu 3.1 

Pb 14.5 

S 4-3 


54       MILL  AND    SMELTER   METHODS. 


CHAPTER  VI. 


Cyanide   Process — Daily  Work. 

The  daily  work  of  a  chemist  in  a  cyanide  plant 
varies  very  much;  there  is  no  standard  western  prac- 
tice that  i  know  of.  In  some  plants  simple  titra- 
tions  for  strength  of  cyanide  with  an  occasional  de- 
termination of  the  gold  in  solution  and  heading  and 
tailing  assays  is  all  that  is  called  for.  On  the  other 
hand,  at  the  large  works  of  the  Metallic  Extraction 
Company  (capacity  10,000  tons  per  month  of  sulpho- 
telluride  ore),  the  routine  determinations  were  as  fol- 
lows: 

Sulphur  in  ores  led  to  the  roasting  furnaces. 

Sulphur,  soluble  and  insoluble,  in  the  roasted 
product. 

Gold  in  the  solutions  entering  and  leaving  the 
precipitators. 

Gold  in  the  final  drains  from  all  leaching  tanks. 

Titrations  of  various  mill  solutions  for  KCN,  alka- 
linity, protective  alkali  and  the  reducing  power  of 
mill  solutions,  etc. 

Bottle  tests  on  all  ores  received  and  on  all  roasted 
ores,  determining  acidity,  extraction  and  cyanide  con- 
sumption. 

A  weekly  analysis  of  the  mill  solutions,  made   up 


MILL   AND   SMELTER   METHODS.       55 

in  the  laboratory  from  proportional  parts  of  the  daily 
samples  received  for  analysis.  This  full  analysis  was 
afterwards  changed  to  monthly  determinations. 

Complete  screen  analysis  of  the  monthly  composite 
sample  (representing  all  the  ores  charged  to  the  leach- 
ing tanks,  and  all  the  tailings  discharged  from  the 
plant),  showing  the  gold  value  contained  at  each 
mesh  from  50  to  200  mesh,  and  the  percentage  of  ex- 
traction. In  addition  to  the  foregoing,  special  re- 
search on  some  line  of  work  always  in  hand.  The 
general  work  of  a  cyanide  chemist  will,  therefore,  lie 
somewhere  between  the  extremes  given  above,  to 
cover  the  ground,  however,  I  give  in  the  following 
notes  all  the  satisfactory  analytical  methods  I  am  ac- 
quainted with,  many  of  them  will  be  needed  daily, 
others  at  much  longer  intervals,  but  in  time  they  may 
all  prove  useful  to  the  cyanide  chemist. 

i.  Titration  of  Cyanide  Solutions. — *This  is  in- 
variably made  by  Liebig's  well  known  method,  de- 
pending on  the  fact  that  when  a  solution  of  nitrate  of 
silver  is  added,  drop  by  drop,  to  the  solution  to  be 
tested,  each  drop  of  the  silver  solution  forms  a  white 
cloud  of  silver  cyanide,  which  disappears  on  agitation 


*  Mr.  J.  McDowell  recommends  for  the  rapid  deter- 
mination of  cyanides,  e.  g.,  in  the  valuation  of  potassium 
cyanide  for  gold  extraction,  titration  with  a  standardized 
solution  of  copper  sulphate  to  which  excess  of  ammonia 
has  been  added.  The  presence  of  chlorides  has  no  influence 
on  the  results. 


56       MILL  AND    SMELTER   METHODS. 

so  long  as  the  free  cyanide  is  in  excess,  the  reactions 
being  as  follows : 

(a)  AgNO3+KCN=AgCN+KNO3. 

(b)  AgCn+KCN=KAg(CN)2. 

The  completion  of  the  reaction  is  shown  by  the 
permanence  of  a  white  turbidity  or  opalescence.  As 
soon  as  the  whole  of  the  free  cyanide  has  been  con- 
verted into  the  double  silver  salt,  a  further  drop  of 
silver  nitrate  in  excess  gives  a  ppt.  of  silver  cyanide 
which  does  not  redissolve  on  agitation. 

(c)  AgNO3+KAg(CN)2=2  AgCN+KNO3. 

From  these  reactions  it  is  evident  that  169.55  parts 
of  AgNO3  are  equivalent  to  130.04  parts  of  KCN. 
Standard  Silver  Nitrate  Solutions. 

Dissolve  6.519  grams  of  AgNQ3  in  I  litre  of  water. 
Every  cc.  of  this  solution  is  equivalent  to  .005  gram 
KCN.  Hence,  if  we  take  50  cc.  of  the  liquid  to  be 
tested,  every  cc.  of  the  standard  AgNO3  added  will 
represent  .01%  KCN. 

From  the  solution  to  be  tested  take,  by  means  of 
a  pipette,  50  cc.,  place  in  a  beaker ;  dilute  with  50  cc. 
H2O;  add  5  cc.  of  a  i%  neutral  solution  of  Ki,*  and 
titrate  with  the  standard  solution.  Or  for  strong  cya- 
nide solutions,  take  13.038  grams  of  pure  crystallized 
nitrate  of  silver,  dissolve  in  distilled  water  and  dilute 


*  The  addition  of  KI  corrects  the  slight  errors  due  to 
the  presence  of  caustic  alkalis,  ammonia,  alkaline  car- 
bonates, chlorides,  ferrocyanides,  thio-cyanates,  thio- sul- 
phates and  perhaps  some  other  salts. 


MILL   AND    SMELTER   METHODS.       57 

to  1,000  cc.  Each  cc.  of  this  solution  is  of  course 
equivalent  to  o.oi  gram  KCN  and  by  taking  10  cc.  of 
the  solution  to  be  tested  each  cc.  of  the  silver  nitrate 
solution  used  in  titration  will  represent  0.10%  of  free 
cyanide. 

It  is  advisable  to  place  about  9  inches  of  rubber 
tubing  over  the  end  of  the  pipette,  as  a  safeguard 
against  drawing  cyanide  solution  into  the  mouth. 
When  the  pipette  is  blown  out,  fill  it  with  an  equal 
volume  of  water  and  add  to  the  cyanide  solution  in 
the  beaker  or  flask.  The  pipette  is  thus  washed  out 
and  ready  for  the  next  measure  of  cyanide  solution. 
The  method  of  titration  for  KCN  herein  given  is  for 
solutions,  say,  over  0.10%.  Below  this  strength  it  is 
not  advisable  to  dilute  with  water. 

The  practice  varies  considerably  in  different  mills, 
both  regarding  the  strength  of  the  silver  nitrate  so- 
lution, and  also  the  amount  of  the  working  cyanide 
solution  taken  for  analysis.  In  some  works  but  10  cc. 
of  solution  is  taken,  and  the  silver  nitrate  standard- 
ized, so  that  each  cc.  equals  o.io  Ibs.  of  cyanide  per 
ton  of  solution,  or  .005%. 

Liebig's  method  works  admirably  with  pure  cy- 
anide solutions,  but  gives  uncertain  and  inaccurate 
results  in  ordinary  working  solutions,  particularly  in 
the  presence  of  zinc.  As,  however,  it  is  generally 
only  necessary  to  obtain  relative  commercial  results, 
and  a  knowledge  of  the  real  strength  of  the  working 


58       MILL  AND    SMELTER   METHODS. 

solution  in  actual  free  KCN  or  its  equivalent  is  not 
essential,  this  method  is  in  general  use. 

Titration  of  Alkalinity. 

2.  KCN  and  other  simple  cyanides  of  the  same 
class  are  alkaline  to  ordinary  indicators.  The  whole  of 
the  alkali  may  be  determined  by  titrating  with  stand- 
ard acid,  using  methyl  orange  as  an  indicator.  With 
phenolphthalein  the  end  point  is  indefinite,  owing  to 
the  faint  action  of  HCN  on  this  indicator. 

The  double  cyanide  of  zinc  and  potassium  is  like- 
wise alkaline  to  methyl  orange. 

For  practical  purposes  it  is  most  important  to 
know  the  alkalinity  exclusive  of  cyanide,  as  it  is  this 
alkali  which  is  chiefly  of  use  in  preventing  the  un- 
necessary waste  of  cyanide  by  reactions  due  to  base 
metal  compounds,  and  to  the  carbonic  acid  of  the  air. 
This  may  be  done  (accurately  in  the  absence  of  zinc) 
by  adding  silver  nitrate  till  a  slight  turbidity  is  pro- 
duced, adding  phenolphthalein  to  this  turbid  solution, 
and  titrating,  without  filtering,  with  N/io  acid.  The 
result  indicates  generally — 

Equivalent  to  hydrates  in  terms  of  N/io  acid  plus 
equivalent  of  half  the  alkali  metal  in  normal  (mono) 
carbonates,  in  terms  of  N/io  acid. 

The  reactions  in  a  typical  case  are : 

KOH+HNO3= KNO3+H2O. 
K2C03+HN03=KHC03+KN03. 

Bi-carbonates     are  .  neutral     to     phenolphthalein, 


MILL   AND   SMELTER   METHODS.       59 

hence  are  not  determined.     They  have  no  protective 
influence  in  this  case. 

When  zinc  is  present  the  total  cyanide  is  first 
determined  by  titration  with  silver  nitrate,  using  the 
alkaline  iodide  indicator.  Another  portion,  say  50  cc. 
of  the  original  solution,  is  now  taken,  an  excess  of 
ferrocyanide  solution  added,  and  then  a  little  more 
silver  solution  than  was  used  in  the  previous  test,  to 
insure  the  complete  conversion  of  all  cyanides  into 
silver  salts.  Phenol-phthalein  is  then  added  and  the 
liquid  titrated  with  standard  acid  as  in  the  previous 
method.* 

j.     Estimation  of  Alkalies. 
Generally  only  two  determinations  are  attempted: 

(1)  What  is  known  as  the  "total  alkali,"  which  may 
be  denned  as  the  equivalent,  in  terms  of  KOH,  of  all 
the  ingredients  which  are  alkaline  to  methyl  orange. 

(2)  What  is  known    as    "protective    alkali."     This 
means,  in  practice,  the  alkalinity  which  the  solution 
shows    to  phenol-phthalein,  after    sufficient    AgNO3 
has  been  added  to  convert  all  the  cyanogen  of  the 
free  cyanides  into  the  double  silver  salt. 

(i)  Titration  of  Total  Alkalies. — A  measured 
quantity  of  the  liquid  is  titrated  with  N/io  acid  (any 
mineral  acid  may  be  used,  but  HNO3  is  preferable), 
a  few  drops  of  a  .1%  solution  of  methyl  orange  being 
used  as  indicator.  If  the  addition  of  acid  should 

*  Proc.  Inst.  Min.  &  Met.,  Vol.  X.,  pp.  29-37,  Green. 


6o       MILL  AND    SMELTER   METHODS. 

cause  a  ppt.  (as  when  Zn,  Cu  or  Ag  salts  are  present) 
it  is  better  to  add  a  moderate  excess  of  acid,  make  up 
to  a  definite  volume,  and  titrate  an  aliquot  portion- 
with  N/io  caustic  alkali.  The  substances  determined 
are:  cyanides,  hydrates,  carbonates,  bi-carbonates, 
sulphides,  zincates,  etc.,  of  the  alkali  and  alkaline 
earth  metals  and  of  ammonium. 

The  double  cyanides  of  Zn,  Ag,  Cu,  and  perhaps 
some  other  metals,  give  ppts.  which  represent  a  con- 
sumption of  acid  proportional  to  the  amount  of  such 
bodies  as  may  be  present,  e.  g. : 

K2Zn(CN)4+2  HNO3  =  Zn(CN)2  +  2  KNO3+ 
2  HCN. 

HCN  and  carbonic  acid  do  not  affect  methyl  or- 
ange. Ferro-cyanides,  ferri-cyanides,"  and  thio-cyan- 
ates  of  potassium,  sodium,  etc.,  are  neutral  to  all  in- 
dicators. 

(2)     Titration  of  Protective  Alkalies. — This  has 
already  been   described.      (See   above.)      All   results 
should  be  calculated  as  the  equivalent  of  KOH. 
4.     Manganese  in  Cyanide  Solutions* 

The  following  process  is  based  on  the  method 
given  by  C.  and  J.  Beringer1  for  the  colorimetric  es- 
timation of  manganese  in  ores  and  compounds  free 
from  chlorides : 


*  J.   C.   Clennell,  Engineering-  and  Mining  Journal,   No- 
vember 24,  1904. 

1  "Text  Book  of  Assaying,"  9th  Edition,  p.  306. 


MILL   AND    SMELTER   METHODS.       61- 

Detection. 

To  100  cc.  of  the  cyanide  solution  to  be  examined 
add  10  cc.  concentrated  nitric  acid.  Heat  to  boiling, 
then  add  gradually  ^  gram  of  lead  peroxide ;  continue 
boiling  for  a  few  minutes,  allow  to  settle,  and  cool. 
The  presence  of  manganese  is  shown  by  the  pink 
color,  due  to  permanaganic  acid.  The  reaction  is  very 
delicate,  quantities  less  than  one  part  in  a  million  of 
solution  being  easily  recognized.  The  test  is  very  simple 
and  rapid.  If  lead  peroxide  is  not  at  hand,  it  may 
easily  be  prepared  by  digesting  red  lead  with  nitric 
acid  and  filtering. 

Estimation. 

An  approximate  quantitative  estimation  may  be 
made  as  follows:  The  contents  of  the  flask  contain- 
ing the  extract  from  100  cc.,  which  will  be  somewhat 
concentrated  by  boiling,  are  again  made  up  to  100  cc. 
or  to  some  other  definite  volume,  with  distilled  water 
recently  boiled  and  cooled.  Stir  well,  and  filter 
through  a  small  paper,  rejecting  the  first  portions  of 
the  filtrate,  say  10  cc.  By  means  of  a  pipette,  draw 
off  an  aliquot  part  of  the  filtrate,  say  50  cc. ;  compare 
the  tint  immediately  with  that  of  an  equal  volume  of 
distilled  water  in  a  similar  vessel,  to  which  the  stand- 
ard permanganate  is  added  drop  by  drop,  with  con- 
stant stirring,  until  the  tints  of  the  liquids  appear 
identical.  A  one-foot  test  tube  of  about  60  cc.  ca- 
pacity may  be  conveniently  used  for  holding  the 


62       MILL  AND   SMELTER   METHODS. 

liquids;   the  color  should  be  observed  against  a  white 
background. 

Standard  Permanganate. 

This  is  made  by  dissolving  0.1435  gm.  of  potassium 
permanganate  in  100  cc.  pure  water,  adding  10  cc. 
pure  concentrated  nitric  acid  and  diluting  to  a  litre. 
One  cc.  of  this  solution  will  contain  0.00005  gm-  °f 
manganese.  Hence,  if  50  cc.  be  taken  for  a  test  on 
an  extract  from  100  cc.  of  the  original  cyanide  solu- 
tion, representing  half  the  original  quantity,  every  cc. 
of  the  standard  solution  used  will  correspond  to 
0.0001%  or  i  part  manganese  in  1,000,000. 
Cautions. 

If  the  test  is  merely  to  be  made  occasionally,  it  i< 
advisable  to  prepare  only  a  small  quantity  of  this 
standard  solution  as  required,  as  it  soon  loses  its 
strength. 

The  success  of  the  process  depends  entirely  on 
the  purity  of  the  reagents  used.  The  distilled  water 
must  be  quite  free  from  organic  matter,  iron  salts  or 
other  reducing  agents.  In  all  cases  a  blank  test  should 
be  made,  using  the  same  quantities  of  nitric  acid,  water, 
lead  peroxide,  etc.,  as  in  the  actual  assay.  The  filtrate 
from  this  should  be  colorless,  but  should  give  a  tint, 
permanent  for  at  least  five  minutes,  on  adding  i  cc.  of 
the  standard  permanganate.  If  this  is  not  the  case, 
a  correction  must  be  made -for  the  reducing  power  of 
the  reagents. 

Ordinary  filter  papers  have  a  slight  action  on  the 


MILL   AND    SMELTER   METHODS.       63 

permanganate,  but  this  does  not  materially  affect  the 
result,  if  the  test  be  carried  out  as  described,  reject- 
ing the  first  part  of  the  filtrate.  Attempts  to  filter 
through  glass  wool  were  not  successful,  as  some  finely 
divided  particles  of  lead  peroxide  invariably  passed 
through  and  obscured  the  tint  of  the  filtrate. 

Influence  of  Manganese  in  Cyanide  Liquors. 

The  presence  of  manganese  may,  in  some  cases, 
exert  an  important  influence  on  extraction  and  pre- 
cipitation, although  the  addition  of  permanaganate 
has  been  advocated  as  an  aid  to  extraction.  It  appears 
to  exist,  at  any  rate,  in  the  cyanide  liquors  obtained 
here,  in  a  very  unstable  form.  It  is  deposited  as  a 
brownish  precipitate-  on  boiling  the  solution,  or  even 
in  some  cases  merely  on  standing.  It  is  thrown  down 
in  a  similar  form  in  the  zinc  boxes  at  ordinary  tem- 
peratures. When  present  in  considerable  quantity  it 
also  interferes  with  the  filtration  of  the  cyanide  by 
silver  nitrate,  sometimes  to  such  an  extent  as  to  ren- 
der the  estimation  of  cyanide  impossible.  The  man- 
ganese always  can  be  removed,  however,  by  treatment 
of  the  solution  with  sodium  sulphide,  the  excess  of  sul- 
phide being  afterwards  removed  by  agitation  with 
carbonate  of  lead  in  the  ordinary  way. 

5.     Estimation  of  Free  Cyanide. 

Differential  Method. — Where  zinc  is  the  only 
metal  present  which  is  capable  of  forming  easily 
decomposable  double  cyanides  of  the  character  of 
K2Zn(CN)4,  a  determination  of  the  so-called  "total 


64       MILL   AND    SMELTER    METHODS. 

cyanide"  by  the  method  given  below,  together  with 
a  determination  of  the  zinc,  enables  us  to  calculate 
the  free  cyanide,  assuming  one  part  of  zinc  equiva- 
lent to  four  parts  of  KCN  converted  into  K2Zn(CN)4. 
In  this  case: 

Free  cyanide  equals  total  cyanide  minus  4xZn. 

The  presence  of  cyanogen,  in  the  form  of  ferro- 
cyanides  or  thiocyanates,  does  not  affect  this  re- 
sult. 

6.     Estimation  of  Total  Cyanide. 

Strictly  speaking,  the  term  "total  cyanide" 
should  indicate  the  equivalent  of  all  the  cyanogen 
contained  in  the  solution.  Practically,  it  is  generally 
taken  to  mean  "the  equivalent,  in  terms  of  KCn,  of 
all  the  cyanogen  existing  in  the  form  of  simple  cy- 
anides, HCN,  and  certain  readily  decomposable  dou- 
ble cyanides,  such  as  that  of  zinc."  Some  other  dou- 
ble cyanides,  such  as  those  of  silver  and  copper,  are 
generally  excluded,  together  with  ferro  and  ferri-cy- 
anides,  thio-cyanates  and  similar  bodies. 

Method  Based  on  Use  of  Alkaline  Iodide  Indicator. 
— An  indicator  is  prepared  by  dissolving  40  grams 
of  caustic  soda  and  10  grams  of  KI  in  water,  and 
making  up  to  a  litre.  Fifty  cc.  of  the  cyanide  solu- 
tion are  taken,  and  5  cc.  of  the  above  indicator  added. 
The  liquid  is  titrated  with  standard  AgNO3  (6.519 
grams  per  litre)  until  a  distinct  yellow  coloration  is 
obtained,  disregarding  any  white  turbidity.  This  lat- 
ter may  sometimes  be  removed  by  adding  NH4OH, 


MILL   AND    SMELTER    METHODS.       65 

which  in  moderate  amounts  does  not  affect  the  ac- 
curacy of  the  test : 

i  cc.  of  AgNO3  used  equals  .01%  KCN  (equiva- 
lent to  total  cyanide). 

7.     Estimation  of  HCN* 

Estimation  of  free  HCN  in  presence  of  alkaline 
cyanides  and  of  zinc  double  cyanides : 

(a)  The  free  cyanide  is  first  estimated  in  the  or- 
dinary way  without  addition  of  alkali.    It  is  assumed 
that  the  presence  of  free  HCN  does  not  affect  this  te- 
sult. 

(b)  Another  portion  of  the  liquid  is  mixed  with 
a  solution  of  potassium  or  sodium  bi-carbonate  con- 
taining no  normal  carbonate  or  free  CO2.    The  mix- 
ture is  titrated  with  AgNO3  as  before,  the  reaction  as 
regards  HCN  being: 

2HKC03+AgN03+2  HCN— KAg(CN)2+KN 
O3+2  CO2+2  H2O. 

The  difference  of  the  two  titrations  gives  the 
equivalent  in  terms  of  KCN  of  the  amount  of  HCN 
present. 

Bi-carbonates  do  not  decompose  K2Zn(CN)4,  but, 
both  titrations  being  subject  to  some  indefiniteness 
as  to  the  finishing  point,  the  method  is  not  very  satis- 
factory. 

*  Bettel.  Proc.  Chem.  and  Met.  Soc.  S.  A.,  Vol.  I., 
p.  165. 


66       MILL  AND    SMELTER   METHODS. 

8.     Estimation  of  F err o cyanide  by  Means  of  Potas- 
sium Permanganate. 

The  ferro-cyanide  is  pptd.  as  Prussian  blue  by 
means  of  an  acidulated  solution  of  ferric  chloride. 
The  ppt.  is  collected  and  washed  thoroughly.  It  is 
then  decomposed  by  hot  caustic  potash,  yielding  ferric 
hydrate  and  potassium  ferro-cyanide,  filtered,  the  fil- 
trate acidulated  with  H2SO4,  and  titrated  with  stand- 
ard permanganate.  The  finishing  point  is  shown  by 
the  change  from  yellow  to  reddish  yel-low.  When  much 
ferro-cyanide  is  present  the  solution  must  be  diluted, 
otherwise  the  end-point  is  not  sharp.  About  100  cc. 
of  H2O  should  be  added  for  every  o.i  grams  ferro- 
cyanide  present.  The  permanganate  must  be  stand- 
ardized against  a  solution  of  pure  potassium  ferro- 
cyanide;  3.16  grams  KMnO4  are  equivalent  to  42.2 
grams  of  K4Fe(CN)6,  3  H2O,  the  reaction  being: 

KMn04+5  K4Fe(CN)6+4  H2SO4=5  K3Fe(CN)6 
+3  K2S04+MnS04+4  H2O. 

A  centi-normal  solution  (0.316  grams  KMnO4  per 
litre)  may  be  conveniently  used. 

The  chief  objection  to  this  method  is  the  difficulty 
of  thoroughly  washing  the  ppt.  of  Prussian  blue.  This 
is  absolutely  necesasry,  as  other  bodies,  e.  g.,  thio-cy- 
anates,  are  almost  invariably  present,  which  would 
likewise  reduce  permanganate  in  acid  solution, 
p.  Estimation  of  Thio-Cyanates  by  Means  of  Iodine* 


*  Hupp  and  Schied.    J.  S.  C.  I.,  1902. 


MILL   AND   SMELTER   METHODS.       67 

This  depends  on  the  fact  that  the  thio-cyanates  re- 
act with  iodine  in  the  presence  of  alkaline  carbonate, 
thus: 

KCNS+KHC03+8  I+3  HaO=KHSO4+6  .HI+ 
C02+KI+ICN. 

A  known  quantity  of  the  solution  is  first  boiled  for 
about  15  minutes  with  |  gram  of  tartaric  acid  in  an 
open  flask  to  get  rid  of  all  HCN,  cooled  and  made  up 
to  100  cc.  Of  this  liquid,  10  cc.  are  then  taken  for 
determination  of  thio-cyanate.  A  measured  amount 
of  N/io  I.,  more  than  sufficient  for  the  reaction,  is 
then  added,  and  about  one  gram  of  NaHCO3.  After 
standing  in  a  stoppered  bottle  for  -J  hour  in  the 
dark,  the  excess  of  I  is  titrated  with  N/io  thio-sul- 
phate. 

Shaking  the  bottle  should  be  avoided  in  order  to 
prevent  the  evolution  of  CO2.  It  is  stated  that  the 
presence  of  cyanogen  iodide  prevents  the  use  of  starch 
as  an  indicator.  It  is  advisable  to  work  with  such 
quantities  that  not  more  than  20  cc.  of  iodine  solu- 
tion are  required.  The  end  of  the  reaction  is  shown 
by  the  disappearance  of  the  yellow  color. 

When  zinc  compounds  of  ferro-cyanides  are  pres- 
ent, a  white  or  bluish  ppt.  occurs  on  boiling  with  tar- 
taric acid,  which  must  be  filtered  off  before  adding 
NaHCO3  and  I. 

10.    Estimation  of  "Total  Cyanogen." 

The  term  "total  cyanogen"  is  here  taken  to  imply 
cyanogen  existing  in  every  form,  whether  as  free  cy- 


68       MILL  AND    SMELTER   METHODS. 

anides,  double  cyanides,  cyanates,  thio-cyanates,  ferro- 
and  ferri-cyanides,  etc. 

(a)  Estimation  by  precipitation  with  AgNO3, 
using  chromate  indicator.  (Based  on  Vielhaber's 
method.) 

This  method  involves  the  separate  determination 
of  the  various  cyanogen  compounds,  and  can  only  be 
regarded  as  a  check  on  the  combined  results.  It  is 
not  applicable  in  presence  of  chlorides,  unless  they 
also  be  separately  determined  and  allowed  for.  Pro- 
tective alkali  must  first  be  neutralized. 

Standard  silver  solution  is  then  run  in  until  the 
reddish  color  of  silver  chromate  becomes  permanent 
on  shaking.  The  indicator  consists  of  a  few  drops  of 
a  strong  solution  of  neutral  (yellow)  potassium 
chromate ;  it  is  advisable  to  insure  the  absence  of 
chlorides  in  the  indicator  by  adding  silver  nitrate  to 
the  chromate  solution  till  a  red  color  is  produced,  and 
allowing  the  ppt.  to  settle.  In  this  process,  cyanides 
(chlorides),  thio-cyanates,  iso-cyanates  and  ferro-cy- 
anides  are  pptd.  as  silver  salts. 

(b)  Total  cyanogen  by  boiling  with  oxide  of  mer- 
cury and  removing  mercury  by  alkaline  sulphide. 
(H.  Rose,  modified.) 

In  case  where  ferro-cyanides  and  similar  com- 
pounds are  present,  the  solution  is  boiled  with  excess 
of  oxide  of  mercury  until  complete  decomposition  is 
effected,  the  liquid  nearly  neutralized  with  HNO3  and 
filtered.  The  filtrate  is  then  mixed  with  Zn(NO3)2, 


MILL   AND    SMELTER   METHODS.       69 

dissolved  in  NH4OH  and  H2S  added  gradually  until 
a  perfectly  white  ppt.  begins  to  appear.  The  ppt.  is 
then  allowed  to  settle,  filtered,  washed  with  very  di- 
lute NH4OH,  and  the  nitrate  titrated  with  AgNO3, 
with  addition  of  KI  as  indicator. 

ii.     Estimation  of  Zinc  by  Decomposition  with  HNO3 
and  HCl,  and  Proceeding  by  Low's 

Method,  Volumetric. 
12.     Estimatio'/i  of  Copper. 

Volumetrically  by  iodide  titration.  Method  of  A. 
H.  Low.  (See  Chapter  on  Smelting.) 

Qualitatively,  the  presence  of  copper  may  readily 
be  detected,  even  in  very  small  quantities,  by  acidu- 
lating the  liquid  with  any  mineral  acid,  and  adding 
a  few  drops  of  dilute  ferro-cyanide  solution,  which 
gives  the  characteristic  reddish-brown  color, 
ij.  Estimation  of  Gold. 

Where  the  gold  or  silver  are  present  in  quantities 
sufficient  to  be  easily  weighed  up  from  one  assay  ton 
of  solution,  30  cc.  are  placed  in  a  lead  foil  tray 
3"X2"Xi">  evaporated  to  dryness,  the  lead  tray 
rolled  up  and  placed  on  the  hot  cupel  and  the  result- 
ing bead  parted  and  weighed  in  the  usual  manner. 
Due  care  must  be  exercised  to  prevent  loss  from  spit- 
ting during  the  last  few  moments  on  the  sand  bath 
or  hot  asbestos  plate.  The  following  method,  while  not 
so  rapid,  is  accurate,  and  is  preferable  in  all  cases 
where  large  quantities  of  solution  must  be  taken  for 
assay : 


70       MILL  AND   SMELTER   METHODS. 

Argall's  Method. — Take  500  cc.  of  the  solution,  or, 
for  greater  convenience,  prepare  a  pipette  to  hold  20 
A.  T.  of  the  solution.  Take  a  tall  beaker,  add  7  grams 
of  zinc  dust  and  pour  in  the  20  A.  T.  of  solution; 
next  add  10  cc.  of  commercial  H2SO4,  stir  well  with  a 
glass  rod  and  cover  with  a  watch  glass.  When  the  ac- 
tion begins  to  fall  off  add  another  10  cc,  of  acid.  The 
precious  metals  will  be  completely  pptd.  in  from  10  to 
20  minutes,  but  the  solution  had  best  be  left  in  the 
beaker  till  the  Zn  is  practically  dissolved,  usually  oc- 
cupying 30  minutes.  A  smaller  quantity  of  Zn  should 
not  be  used,  and  if  the  gold  and  silver  is  over  0.05  ozs. 
per  ton,  10  grams  should  be  taken. 

When  action  is  completed,  filter,  add  3  grams  of 
SiO2  to  the  residue  on  the  filter  paper,  fold,  place  in  a 
10  gram  crucible,  incinerate  in  the  muffle,  remove 
crucible,  and  when  cool  add  10  grams  each  of  flux 
and  litharge;  thoroughly  mix  in  the  crucible,  fuse, 
cupel,  weigh,  and  part  in  the  usual  manner.  The  flux 
used  consists  of  42  parts  potash,  84  NaHCO3,  2  borax- 
glass  and  9  of  flour.  Should  copper  be  present  in  the 
solution,  a  larger  proportion  of  flux  will  be  required, 
and  scorification  may  be  necessary. 
Chiddey  Method. 

Five  assay  tons  of  the  solution  is  placed  in  a 
beaker  and  brought  nearly  to  boiling.  Add  12  cc.  of 
a  saturated  solution  of  lead  acetate  (must  be  acid, 
with  acetic  acid  to  prevent  the  precipitation  of  lead 
as  a  hydrate),  then  add  -J  gram  of  zinc  dust,  allow 


MILL   AND    SMELTER   METHODS.       71 

to  stand  for  a  few  minutes  and  then  add  12  cc.  HC1. 

When  the  sponge  is  well  formed  add  a  small  piece 
of  aluminum  foil  to  precipitate  any  remaining  lead, 
and  which  keeps  the  sponge  already  formed  from 
breaking  up.  When  the  excess  of  zinc  appears  to 
have  dissolved  pour  about  10  cc.  of  HC1  upon  the 
sponge.  Remove  and  decant  the  liquor,  squeeze  the 
sponge  together  with  a  rubber  policeman  and  place 
it  upon  a  piece  of  lead  foil  about  two  inches  square. 
Squeeze  as  much  moisture  as  possible  from  the  sponge, 
fold  the  lead  over  it  and  roll  it  into  a  ball,  making  a 
small  hole  for  steam  to  escape.  Place  in  a  hot  cupel. 
14.  Estimation  of  Silver. 

In  the  Argall  method  for  gold  we  determine  the 
combined  weight  of  gold  and  silver,  from  which  the 
silver  may  be  calculated  after  parting  the  bead  with 
HNO3  and  weighing  the  gold.  I  have  not  tested  this 
method  where  large  amounts  of  silver  were  present  in 
solution,  but  up  to  16  oz.  per  ton  I  know  it  gives  cor- 
rect results  and  without  the  formation  of  silver  sul- 
phates. If  on  richer  solutions  this  was  feared,  hy- 
drochloric acid  could  be  substituted  for  the  sul- 
phuric. 

The  following  method,  recommended  by  Alfred 
Chiddey,*  has  not  been  tested,  though  it  is  claimed  to 
give  higher  results  than  the  evaporation  process  in 
ordinary  use.  The  proportion  of  silver  to  gold  in  the 


*  Engineering     and     Mining    Journal,     March    2S,    1903, 
p.   473. 


72       MILL  AND    SMELTER   METHODS. 

solutions  on  which  Mr.  Chiddey  used  it  is  10  to  I, 
and  in  case  of  nearly  pure  gold  solutions  the  addi- 
tion of  a  known  quantity  of  silver  nitrate  dissolved  in 
cyanide  is  suggested.  Introduce  into  a  porcelain  dish 
four  assay  tons,  or  more,  of  the  solution  to  be  as- 
sayed ;  add  10  cc.  of  a  10%  solution  of  acetate  of  lead, 
then  4  grams  of  zinc  shavings ;  boil  a  minute,  add  20 
cc.  of  hydrochloric  acid.  When  the  action  has  ceased 
boil  again ;  wash  the  spongy  lead  with  distilled  water ; 
transfer  it  with  a  stirring  rod  to  a  piece  of  filter  pa- 
per; squeeze  into  a  compact  lump  and  place  in  a  hot 
cupel.  The  mouth  of  the  muffle  should  contain  a 
piece  of  dry  pine  wood,  so  that  the  muffle  is  filled  with 
flame  at  the  moment  of  introducing  the  spongy 
lead. 

15.     Purple  of  Cassius  Test  for  Gold* 

Precipitate  the  gold  with  zinc  dust;  dissolve  the 
excess  of  zinc  with  dilute  sulphuric  acid ;  dissolve  the 
gold  in  aqua  regia  and  add  a  few  drops  of  tin  chloride 
Compare  the  color  obtained  with  a  standard. 

The  cyanide  solution  to  be  tested  must  be  strength- 
ened by  the  addition  of  a  few  drops  of  a  strong  cy- 
anide solution,  say  of  15%  KCN,  so  that  the  solution  to 
be  assayed  may  contain  i%  free  KCN.  To  200  cubic 
centimeters  of  the  solution  add  about  I  gram  of  zinc 
dust.  Heat  the  solution  to  boiling  point.  Filter  off 
the  cyanide  solution.  Add  to  the  remaining  zinc  dust 


*  A.  Prister.     Journal  of  the  Chemical  and  Metallurg- 
ical Society  of  South  Africa. 


MILL   AND    SMELTER    METHODS.       73 

about  20  cubic  centimeters  of  dilute  (10%)  sulphuric 
acid  and  dissolve  all  the  zinc  by  gently  warming.  Fil- 
ter off  through  the  same  filter  the  solution  of  zinc 
sulphate  formed.  Dissolve  the  residual  metals  in  10 
cc.  of  aqua  regia  and  pass  while  boiling  repeatedly 
through  the  same  filter,  and  collect  the  gold  solution 
in  a  test  tube. 

To  the  gold  solution  a  few  drops  of  stannous  chlo- 
ride are  added  after  the  solution  has  been  cooled  by 
holding  the  test  tube  in  water. 

If  the  solution  is  rich  in  gold,  the  purple  of  Cas- 
sius  coloration  will  appear  directly ;  if  it  is  poor,  the 
color  will  require  a  few  minutes  to  become  evident. 
The  aqua  regia  used  can  be  made  by  mixing  six  parts 
of  strong  hydrochloric  acid,  two  parts  of  strong  nitric 
acid  and  six  parts  of  distilled  water. 

16.    Qualitative  Detection  of  Gold. 

The  presence  of  gold  in  quantities  less  than  o.i 
mgr.  may  be  detected  in  cyanide  solution  by  acidulat- 
ing, boiling  till  most  of  the  HCN  is  expelled,  then 
adding  KC1O3  and  again  boiling  till  most  of  the 
chlorous  gases  are  driven  off,  and  finally  adding  stan- 
nous chloride,  which  gives  the  well  known  purple  of 
Cassius.  The  final  solution  should  not  be  too  strongly 
acid,  or  the  color  may  not  appear.  It  frequently  be- 
comes more  marked  on  allowing  to  stand  for  some 
time. 
17.  Estimation  of  the  Reducing  Power  of  Solution. 

Definition:     The  reducing  power  of  a  solution  is 


74       MILL  AND   SMELTER   METHODS. 

the  number  of  cubic  centimeters  of  N/io  perman- 
ganate which  must  be  added  to  give  a  permanent  col- 
oration with  i  cc.  of  the  solution  to  be  tested,  a  suffi- 
cient amount  of  free  sulphuric  acid  to  be  present  in 
every  case. 

Indirect  Estimation  by  Adding  Excess  of  Perman- 
ganate.* 

Acidify  the  solution  to  be  tested  and  add  a  mod- 
erate excess  of  permanganate,  allow  to  stand  for  some 
time,  then  add  an  excess  of  potassium  iodide  to  the 
pink  liquid  until  the  color  changes  to  brownish  yel- 
low; in  this  reaction  iodine  is  liberated  in  proportion 
to  the  excess  of  permanagante  present.  Titrate  the 
iodine  with  standard  thiosulphate,  using  a  starch  in- 
dicator prepared  with  the  addition  of  caustic  soda. 
Deduct  the  equivalent  of  the  iodine  thus  found,  in 
terms  of  standard  permanganate,  from  the  total 
amount  of  permanganate  added,  and  the  remaining 
permanganate  corresponds  to  the  reducing  agents 
present  in  the  solution  tested. 

To  standardize  the  permanganate,  add  an  excess 
of  potassium  iodide  to  a  measured  volume  and  deter- 
mine the  amount  ot  thiosulphate  required  to  destroy 
the  color. 

Standard  permanganate,  3.16  grams  per  litre.  So- 
dium thiosulphate,  24.8  grams  per  litre.  Potassium 
iodide,  16.6  grams  per  litre. 


*J.  E.  Clennell,  "The  Chemistry  of  Cyanide  Solutions." 


MILL   AND   SMELTER   METHODS.       75 

18.    Estimation  of  Alkaline  Sulphides* 

On  adding  an  excess  of  a  solution  of  the  double  cy- 
anide of  silver  to  a  liquid  containing  alkaline  sul- 
phides, free  cyanide  is  produced  in  proportion  to  the 
amount  of  sulphide  present. 

2  KAg(CN)2+K2S=Ag2S+4  KCN. 

Filter  off  the  precipitated  sulphide  of  silver  and 
estimate  the  cyanide  by  adding  potassium  iodide  and 
titrating  in  the  usual  way  with  silver  nitrate. 

If  there  be  any  cyanide  present  in  the  original 
liquid  it  may  be  separately  determined  after  treat- 
ment with  lead  carbonate  and  deducted  from  that 
previously  found. 

Prepare  the  silver  double  cyanide  by  adding  sil- 
ver nitrate  to  a  solution  of  0.5%  KCN  until  a  slight 
permanent  turbidity  is  formed.     Allow  to  stand  for 
a  time,  then  filter. 
Estimation  of  Sulphides   by   Colorimetric   Test  with 

Sodium  Nitro-prusside. 

The  following  method  by  Dr.  J.  Loevey  of  Johan- 
nesburg is  quite  simple  and  can  be  rapidly  carried 
out:  The  required  solutions  are :  (a)  Standard  so- 
dium sulphide,  Na2S  40  grams  and  NaOH,  0.2  gram, 
dissolve  to  one  liter,  i  cc.  of  this  solution=o.oo53 
gram,  (b)  Standard  zinc  sulphate:  ZnSO47  H2O, 
44.15  grams  per  litre.  I  cc.=o.oi  gram  Zn.  (c) 
Sodium  nitroprusside :  5  grams  of  the  salt  dissolved 


*  J.  E.   Clennell,  "The  Chemistry  of  Cyanide  Solutions." 


76       MILL   AND    SMELTER   METHODS. 

in  100  cc.  of  water,  to  which  5  drops  of  5%  cyanide 
are  added.  Sodium  nitroprusside  is  prepared  in  the 
following  manner:  Dilute  concentrated  nitric  acid 
with  an  equal  volume  of  water  and  mix  with  pow- 
dered potassium  ferrocyanide  in  the  proportion  of  2 
parts  K4FeCN63H2O  to  5  parts  diluted  HNO3.  Warm 
on  the  water  bath  until  the  liquid  gives  a  dark  green 
or  slate  colored  precipitate  instead  of  blue,  with  fer- 
rous sulphate.  It  is  then  cooled,  neutralized  with 
sodium  carbonate  and  filtered.  Two  similar  cyaniders 
are  taken.  In  one  is  placed  a  measured  volume  of  the 
liquid  to  be  tested,  and  in  the  other  an  equal  volume 
of  pure  cyanide  solution  free  from  sulphide,  and  con- 
taining approximately  the  same  amount  of  free  cya- 
nide as  the  first.  One  cc.  of  5%  solution  of  sodium 
nitro-prusside  is  now  added  to  each.  If  the  liquid 
in  the  first  cylinder  contains  sulphides,  a  coloration 
is  produced,  while  that  in  the  second  cylinder  remains 
colorless.  Sodium  sulphide  solution  (about  4%)  is  now 
run  in  from  a  burette,  drop  by  drop,  to  the  second 
cylinder  till  the  color  in  the  two  vessels  is  the  same. 
The  amount  used  gives  the  amount  of  sulphide,  calcu- 
lated as  Na2S,  present  in  the  first  cylinder.  The  so- 
dium sulphide  solution  should  be  carefully  standard- 
ized ;  this  may  be  done  by  any  of  the  ordinary  meth- 
ods, as,  for  example,  by  means  of  a  zinc  sulphate  solu- 
tion of  known  strength,  using  ferric  hydrate  as  exter- 
nal indicator. 


MILL   AND   SMELTER    METHODS.       77 

Qualitative  Tests  for  Alkaline  Sulphides. 

(a)  Place  a  few'  drops  of  the  clear  solution  on  a 
piece  of  clean,  bright  silver,  or  agitate  the  solution 
gently  with  a  piece  of    clean  silver  foil;    if  sulphides 
are  present  the  silver  will  be  blackened. 

(b)  The  most  delicate  test,   however,   is    nitro- 
prussides. 

Add  a  little  of  the  nitro-prusside  solution  to  the 
cyanide  solution  to  be  tested;  if  an  alkaline  sulphide 
is  present  the  solution  will  assume  a  purple  color. 

The  following  method  for  estimating  cyanogen  in 
commercial  cyanide  is  said  to  be  more  accurate  than 
Liebig's  and  is  recommended  by  Adair.* 

The  method  to  be  described  was  originally  devised 
for  the  estimation  of  ferro-cyanide  in  pot-metal  (a 
very  impure  product).  It  can  be  readily  adapted  for 
the  estimation  of  cyanogen  in  commercial  cyanide, 
and  is  preferable  to  the  silver  methods  for  this  pm- 
pose  because,  although  not  quite  so  quick,  only  the 
useful  cyanide  is  estimated.  Cyanates,  sulpho-cy- 
anides,  sulphides  and  chlorides,  even  in  large  percent- 
ages, do  not  sensibly  affect  the  result. 

The  outline  of  the  method  is  to  convert  the  cy- 
anide as  such  into  ferro-cyanide ;  next  to  oxidize  with 
KMnO4,  in  the  presence  of  H2SO4.  The  ferro-cy- 
anide is  oxidized  to  ferri-cyanide  only,  whereas  cy- 
anates,  sulpho-cyanides  and  other  impurities  are  either 
distinctively  oxidized  or  converted  into  substances 

*  Jour,  of  the  Chem.  Soc.  of  So.  Africa,  Jan.,  1903. 


78       MILL  AND    SMELTER   METHODS. 

which  do  not  interfere  with  the  final  steps  of  reducing 
the  ferri-cyanide  to  ferro-cyanide,  and  the  titration  of 
the  latter  with  KMnO4  in  acid  solution. 

Estimations  can  be  made  in  15  minutes,  and  con- 
cordant results  are  obtained  in  different  operators' 
hands. 

The  solutions  required  are: 

25%  caustic  alkali. 

20%  H2SO4  pure. 
Saturated  solution  of  KMnO4,  approximate  strength 

only. 
Saturated  solution  of    FeSO4,  approximate  strength 

only. 

N/io  KMnO4.  i  cc.  equals  .156  grams  total  Cn,  or 
more  convenient  strength,  I  cc.  equals  .100  total  CN. 

The  solution  is  standardized  with  K4Fe(CN)6+ 
3  Aq.  3  grams  are  dissolved  in  300  cc.  H2O  and  15  cc. 
of  the  20%  acid  are  added. 

88oX3 

=Value  CN  in  grams  per  cc. 

i57-9Xcc.  consumed 

ip.    Method. 

Ten  grams  of  the  cyanide  are  weighed  into  a  litre 
flask  and  about  200  cc.  water  used  to  dissolve  it;  add 
2  cc.  of  the  alkali  solution  and  a  quantity  of  Ire 
FeSO4  solution  equal  to  12  grams  FeSO4+7  Aq.  Add 
the  latter  5cc  at  a  time  and  shake  well. 
6  KCN&FeS04+alkali=K4Fe  ( CN )  6+K2SO4+alkali. 

The  reaction  is  immediate.    Add  H2SO4  and  Prus- 


MILL   AND   SMELTER   METHODS.       79 

sian  blue  is  formed.  Then  15  cc.  H2SO4  and  saturated 
solution  of  permanganate  until  the  color  remains  per- 
sistent ;  the  color  can  be  seen  through  the  edges. 

One  or  two  cc.  or  more  in  excess  does  not  matter. 
The  above  quantity  of  acid  is  enough  for  each  gram  of 
KMnO4  added,  but  if  more  than  I  gram  KMnO4  is 
used,  acid  must  be  added  in  the  same  proportion,  viz : 
15  cc.  to  each  gram  of  KMnO4  used.  If  much  sulpho- 
cyanide  is  present  allow  to  stand  15  minutes,  and,  if 
necessary,  a  further  addition  of  KMnO4  may  be  re- 
quired. The  reaction  is: 

5  K4Fe(CN)6+4H2S04+KMn04=5  K3Fe(CN)6 
+3  K2SO4+MnSO4+4  H2O. 

Next  add  FeSO4  solution  in  quantity  equal  to  15 
grams  and  immediately  15  cc.  alkali  solution.  The  so- 
lution must  be  strongly  alkaline.  Shake  thoroughly 
and  make  up  to  the  mark,  again  mixing  thoroughly. 

Filter  through  a  large  folded  filter.  The  titration 
is  completed  by  taking  500  cc.  or  an  aliquot  portion, 
adding  20  cc.  H2SO4  and  adding  the  standard  KMnO4. 

The  influence  of  the  precipitate  on  the  results  is 
small.  It  may  be  ascertained  by  testing  a  weighed 
portion  of  pure  K4Fe(CN)6,  3  H2O,  adding  the  quanti- 
ties of  solutions  as  for  an  impure  sample.* 

Impurities  in  commercial  cyanide  may  be  detected 
in  the  following  manner.*  Potassium  cyanate  will  dis- 
solve in  alcohol  of  specific  gravity  0.849,  and  this  so- 


t  Allen,  Engineering  and  Mining  Journal,  Aug.  15,  1903, 
p.  239. 


8o       MILL  AND    SMELTER   METHODS. 

lution,  on  addition  of  hydrochloric  acid,  will  evolve 
carbon  dioxide.  Or,  on  adding  water  to  the  alcoholic 
solution,  and  boiling  off  the  alcohol,  the  liquid  will 
give  a  precipitate  of  calcium  carbonate  with  calcium 
chloride.  Cyanate  may  also  be  detected  by  the  follow- 
ing application  of  Blomstrand's  color  reaction:  A 
strong  solution  of  the  sample  is  decomposed  by  passing 
carbon  dioxide  through  it  until  no  more  hydrocyanic 
acid  is  evolved.  By  these  means  E.  A.  Schneider 
(Journal,  Society  Chemical  Industry,  1895,  p.  887) 
found  that  3  grams  of  potassium  cyanide  were  decom- 
posed in  45  minutes.  To  the  resulting  liquid  Schnei- 
der adds  sufficient  95%  alcohol  to  precipitate  the  pot- 
assium carbonate  formed.  The  filtrate  is  then  slightly 
acidified  with  acetic  acid,  and  some  cobalt  acetate  so- 
lution added.  An  intense  blue  color,  due  to  the  forma- 
tion of  the  double  cyanide  of  cobalt  and  potassium,  is 
produced,  which  renders  easy  the  detection  of  as  little 
as  0.35%  of  cyanate.  If  present  in  smaller  quantities, 
more  of  the  cyanide  must  be  taken,  dissolved  in  the 
smallest  possible  quantity  of  water,  and  the  greater 
part  of  the  cyanide  precipitated  by  the  addition  of 
absolute  alcohol.  The  filtrate  is  then  treated  with  car- 
bon dioxide,  and  tested  as  before. 

Chlorides  may  be  detected  by  silver  nitrate,  added 
in  excess,  which  throws  down  silver  cyanide  as  a  white 
curdy  precipitate.  They  may  be  determined  by  Sie- 
bold's  volumetric  method. 

L.  Siebold  has  shown  that  chlorides,  when  present, 


MILL   AND    SMELTER    METHODS.       81 

may  be  conveniently  determined  in  the  same  liquid  in 
which  the  cyanide  has  been  estimated  by  neutralizing 
the  excess  of  free  alkali  (which  should  not  be  am- 
monia) by  the  cautious  addition  of  dilute  nitric  acid, 
adding  a  few  drops  of  a  solution  of  neutral  potassium 
chromate  and  continuing  the  addition  of  the  silver  so- 
lution until  the  red  tint  due  to  the  formation  of  silver 
chromate  remains  permanent.  If  cyanide  only  be 
present,  the  volume  of  silver  solution  now  required 
will  be  exactly  equal  to  that  previously  employed  to 
obtain  a  permanent  turbidity,  whereas  any  excess  over 
this  amount  represents  the  silver  solution  correspond- 
ing to  the  chlorides  present. 

Formates,  if  present,  will  cause  the  salt  to  blacken 
on  ignition.  They  may  be  detected  more  certainly  by 
precipitating  the  cold  dilute  solution  of  the  samplo 
with  excess  of  silver  nitrate  solution,  filtering  cold  and 
heating  the  clear  liquid.  In  presence  of  a  formate, 
metallic  silver  will  be  precipitated.  The  nitrate  from 
the  precipitate  produced  by  silver  nitrate  will  also  give 
a  red  color  with  ferric  nitrate  or  sulphate  if  a  formate 
be  present. 

Carbonates  will  remain  insoluble  on  treating  the 
sample  with  hot  alcohol  of  0.849  specific  gravity. 

Silicates  can  be  detected  and  estimated  in  the  ordi- 
nary way  by  evaporation  to  dryness  with  hydrochloric 
acid,  the  residue  insoluble  in  acidulated  water  being- 
silica. 

Sulphates  are  detected  by  the  formation  of  a  white 


82       MILL   AND    SMELTER    METHODS. 

precipitate  on  adding  barium  chloride  to  a  solution  of 
the  sample  previously  acidulated  by  hydrochloric 
acid. 

Sulphides  will  give  a  black  precipitate  with  mer- 
curic chloride  and  a  yellow  precipitate  with  a  solution 
of  cadmium.  They  can  be  separated  by  agitating  the 
solution  with  lead  carbonate. 

Free  ammonia  can  be  recognized  by  the  smell  and 
determined  by  treating  the  solution  with  an  alkaline 
solution  of  sodium  hypo-bromite  and  measuring  the 
nitrogen  gas  evolved. 

20.    Estimation   of  Bromo   Cyanogen   and  Potassium 
Bromate. 

An  N-io  solution  of  sodium-thio-sulphate  is  used 
in  the  determination  of  bromo  cyanogen  and  potas- 
sium bromate.  This  solution  will  contain  12.4  grams 
of  Na2S2O3  5  H2O,  therefore  I  cc.  will  be  equivalent 
to  0.00265  gram  of  bromo  cyanogen  or  to  0.00141.' 
grams  of  potassium  bromate. 

Potassium  Bromate. — Take  200  milligrams  of  the 
dry  salt,  dissolve  in  100  cc.  of  distilled  water,  then 
add  about  15  to  20  cc.  of  dilute  hydrochloric  acid, 
and  3  to  5  grams  of  potassium  iodide.  Iodine  will  be 
liberated  and  the  solution  is  then  titrated  to  colorless- 
ness  by  N-io  sodium-thio-sulphate  solution.  For 
more  accurate  work  starch  solution  should  be  used  as 
an  indicator. 

Bromo  Cyanogen. — Take  5  to  10  cc.  of  the  solu- 
tion to  be  estimated,  dilute  with  25  to  50  cc.  of  dis- 


MILL   AND    SMELTER    METHODS.       83 

tilled  water,  add  5  cc.  of  dilute  hydrochloric  acid  and  4 
to  5  grams  of  potassium  iodide,  iodine  is  liberated  and 
the  solution  is  then  titrated  to  colorlessness  by  N-io 
sodium-thio-sulphate  solution,  or  starch  solution  can 
be  used  as  an  indicator. 

The  presence  of  potassium  cyanide  in  the  solution 
will  not  interfere  with  the  titration  for  bromo  cyano- 
gen, consequently  the  method  can  be  used  on  mill  so- 
lutions and  it  is  also  noteworthy  that  in  the  estima- 
tion of  potassium  cyanide  in  the  same  solutions  with 
silver  nitrate,  in  the  usual  way,  bromo  cyanogen  does 
not  interfere  with  the  test,  except  in  the  presence  of 
cyanogen,  due  to  the  reactions  between  bromo  cyano- 
gen and  potassium  cyanide,  and  in  this  case  the 
method  gives  somewhat  lower  results. 


84       MILL   AND    SMELTER    METHODS. 


CHAPTER  VII. 


Estimation    of   Oxygen    in    Working   Cyanide   Solutions. 


It  is  a  well  known  fact  that  in  the  cyanide  process, 
as  ordinarily  used,  the  solution  must  contain  oxygen 
in  order  to  dissolve  the  gold.  Realizing  the  import- 
ance of  this,  about  ten  years  ago  the  Chemical  and 
Metallurgical  Society  of  South  Africa  offered  a  gold 
medal  to  anyone  who  should  find  a  method  of  actually 
determining  the  oxygen  in  a  working  cyanide  solution. 
This  medal  was  awarded  to  Mr.  Andrew  F.  Crosse,  in 
January,  1899. 

The  following  description  of  his  method  is  adapted 
and  condensed  from  Mr.  Crosse's  articles  published  in 
Volume  II.  of  the  Transactions  of  the  Chemical  and 
Metallurgical  Society  of  South  Africa,  pages  396,  419 
and  476. 

Estimation  of  Oxygen  in  Working  Cyanide  Solutions. 
By  A.  F.  Crosse. 

The  ordinary  working  cyanide  solution  contains 
substances  which  prevent  the  direct  application  of 
Thresh's  well  known  method  for  the  determination  of 
oxygen  dissolved  in  water,  as  described  in  Sutton's 
Volumetric  Analysis,  pages  277-283.  By  preliminary 
treatment,  however,  these  substances  can  either  be  re- 
moved or  neutralized,  without  affecting  the  oxygen 


MILL   AND    SMELTER    METHODS.       85 

present  in  the  solution,  leaving  it  amenable  to  Thresh's 
method.  This  method  is  based  on  the  fact  that  iodir.e 
is  liberated  when  potassium  nitrate  and  sulphuric  acid 
are  brought  together  in  water  containing  free  O,  16 
parts  of  O  liberating  254  parts  of  I. 

Apparatus  Necessary. 

i  "Winchester  quart"  white  glass  bottle,  with  ac- 
curate fitting  glass  stopper  and  of  known  capacity. 
— about  2,\  litres. 

i   Smaller  glass  bottle — 16  oz. 

i   50  QC.  burette,  for  ZnSO4  solution. 

1  Rubber  stopper,  with  two  holes,  to  fit  large  bottle. 

2  293  cc.  Thresh's  separatory  tubes,  ground  glass  stop- 

pers. 

i   Large,  wide-mouthed  bottle,  white  glass, 
i   Rubber  stopper,  with  4  holes,  to  fit  same, 
i   50  cc.  burette  for  hyposulphite  solution. 
i   Small  pipette  with  stopcock  for  NaNO2,  KI  solution, 
i   Small  pipette  with  stopcock  for  H2SO4  solution, 
i   350  cc.    flask. 

Beakers,  glass  tubing,  rubber  tubing,  etc. 

Solutions. 

ZnSO4,  7  H2O.    200  grams  made  up  to  i  litre ;  i  cc. 
solution=2  grams  ZnSO4,  7  H2O. 
Phenolphthalein . 

Na2S2O3 — 7.75  grams  per  litre  water. 
Bromine  water. 


86       MILL   AND    SMELTER    METHODS. 

(   NaNO2  .5  grams. 
KI  and  sodic  nitrite  solution     :   KI          20  grams. 

(  H,O     ioo  cc. 
KI  and  starch. 

The  Method  Consists  in : 

First— Adding  KOH. 

Second — Adding  ZnSO4,  7  H2O. 

Third — Determining  hyposulphite  required  by 
Thresh's  method  with  clear  solution  decanted  from 
precipitates  formed  in  the  closed  bottle. 

Fourth — Qualitative  tests  for  nitrites. 

Fifth — Correction  for  nitrites  and  reagents  used. 

The  Winchester  quart  and  the  16  oz.  bottle  are 
filled  with  the  solution  to  be  tested;  the  contents  of 
the  latter  to  be  used  for  preliminary  work,  and  the 
former  for  the  actual  analysis. 

Take  ioo  cc.  from  the  small  bottle,  add  a  few  drops 
of  phenolphthalein  and  run  in  the  20%  solution  of 
ZnSO4  until  the  alkaline  action  has  disappeared,  which 
is  seen  at  once  by  the  characteristic  magenta  color  hav- 
ing vanished.  It  is  advisable  to  filter  the  solution  after 
the  first  disappearance  of  the  pink  coloration,  as  the 
ppt,  carries  down  the  coloring  matter.  The  amount 
required  for  the  Winchester  quart,  the  contents  01 
which  are  known,  can  then  be  calculated. 

Add  5  or  6  grams  of  solid  KOH  to  the  Winchester 
quart,  and,  when  dissolved,  add  the  required  amount  of 
solid  ZnSO6,  7  H,O,  taking  care  not  to  allow  any  air  to 
enter  the  solution.  Replace  the  stopper,  shake  the  bot- 


MILL   AND    SMELTER    METHODS.       87 

tie  well  and  let  it  stand  for  some  time,  so  that  the  floc- 
culent  ppt.  of  cyanide  of  zinc  may  settle,  and  obtain 
a  clear  supernatant  liquid.  If  possible,  let  stand  over 
night.  When  the  ppt.  has  settled  sufficiently,  the 
liquid  is  siphoned  off.  Use  a  two-holed  rubber  stopper, 
with  a  siphon  passing  through  one  hole,  and  a  short, 
bent  tube  through  the  other,  and  start  the  action  by 
blowing  through  this  bent  tube,  as  one  would  use  a 
wash  bottle.  The  end  of  the  siphon  in  the  liquid  should 
have  a  small  bag  of  lint  tied  over  it,  to  prevent  the 
carrying  away  of  any  small  particles  of  ppt.  In  this 
way,  fill  the  two  293  cc.  separatory  tubes  and  put  them 
aside  for  the  present.  Draw  off  the  same  quantity, 
293  cc.  into  a  beaker,  add  I  cc.  H2SO4  (half  acid  and 
half  water)  and  i  cc.  of  iodide  of  potassium  and  starch. 
From  a  burette,  add  carefully,  drop  by  drop,  dilute 
bromine  water  (i  bromine  water  to  2  of  water)  till  a 
blue  color  is  obtained,  and  note  the  number  of  drops. 

Take  this  tube  with  the  solution  to  be  tested,  add  i 
cc.  NaNO2  and  KI  solution  and  i.o  cc.  H2SO4  (half 
acid,  half  water)  and  the  number  of  drops  of  bromine 
water  required,  put  in  the  stopper  and  turn  over  the 
tube  several  times.  Iodine  is  at  once  set  free  in  pro- 
portion to  the  oxygen  in  the  solution,  and  is  ready  to 
be  determined  by  titration  with  hyposulphite,  accord- 
ing to  Thresh's  method. 

The  wide-mouthed  glass  bottle,  having  a  rubber 
stopper  pierced  with  four  holes,  is  here  used,  and  coal 
gas,  or  CO2,  must  be  passed  through  it  during  the  ex- 


88       MILL   AND    SMELTER    METHODS. 

periment.  The  CO2  must  be  purified  by  passing- 
through  a  potassium  iodide  and  freed  from  oxygen. 
The  tube  containing  the  solution  is  inserted  through 
the  third  hole  and  the  hyposulphite  burette  through 
the  fourth.  Coal  gas  (or  CO2)  is  passed  through  the 
bottle  for  15  minutes,  and  then  the  KCN  solution  is 
allowed  to  flow  into  the  bottle  and  also  a  few  drops 
of  starch  solution,  which  becomes  blue  at  once.  The 
stopcock  is  turned  off  and  the  free  iodine  is  deter- 
mined by  dropping  in  hyposulphite  solution,  slowly, 
until  the  blue  color  disappears ;  7.75  grams  of  hypo- 
sJphite  in  I  litre  of  water  gives  a  solution,  I  cc.  of 
which  corresponds  to  .25  milligrams  of  O.  A  correc- 
tion must  be  made  for  the  O  in  the  reagents  used. 

Nitrate  of  potash  (or  soda)  is  oxidized  by  the  ad- 
dition of  bromine  water,  and  liberates  iodine.  To  de- 
termine the  correction  necessary  for  this  iodine,  take  a 
350  cc.  extra  strong  flask,  and  pour  into  it  the  same 
amount  of  solution  as  taken  for  the  analysis.  Add  a 
few  drops  of  KOH  and  close  the  flask  with  a  one-hole 
rubber  stopper  containing  a  glass  tube  with  stopcock. 
Boil  the  solution  for  several  minutes  and  close  the 
cock.  Cool  the  flask,  pour  the  contents  into  the  tube, 
add  i  cc.  of  iodide  of  potassium  and  nitrate  solution, 
and  i  cc.  dilute H2SO4  (half  and  half) .  Place  the  burette 
in  the  stopper  of  the  wide-mouthed  glass  bottle,  turn 
on  the  gas,  and  after  10  minutes  run  the  solution  into 
the  bottle ;  add  a  few  drops  of  starch,  and  titrate,  as 
before.  The  quantity  required  will  give  the  correc- 


MILL   AND    SMELTER    METHODS.       89 

tion  for  the  nitrates  in  the  solution,  and  also  for  the 
reagents  used,  as  the  same  amount  of  H2SO4,  and  also 
the  same  amount  of  KI,  containing-  potassium  nitrite, 
is  used  in  each  case. 

Calculations. 
Let 

L  =  capacity    of    Thresh's    tube,    minus    reagents 
used  =  293  —  3  =  290  cc. 

X  =  milligrams  of  oxygen  per  litre  in  the  solution 
under  examination. 

M  =  correction    for    nitrites    and    oxygen    in    the 
reagents  used. 

N  =  hyposulphite  of  soda  used  in  the  final  deter- 
mination. 
Then, 

(N  —  M)X  .25X1000 

-  =X. 
L 

.  In  actual  analysis  the  following  results  were  ob- 
tained : 

N  =  10.2  cc.     M  =  2.8cc. 
(10.2  —  2.8)  X  .25X1000  =6.3  mg.  O  per  litre. 


290  =.0063  grams  O  per  litre. 

Precautions. 

In  all  stages  of  the  analysis  care  should  be  taken 
to  prevent  the  addition  of  air  to  the  solution. 

The  bromine  water  in  the  lower  part  of  the  bur- 
ette under  the  stopcock  quickly  detoriates  by  loss  of 


90       MILL   AND    SMELTER    METHODS. 

Br,  and  should,  therefore,  be  run  off  before  beginning 
the  titration. 

The  following  shorter  method  is  recommended  bN 
Prister:* 

The  oxygen  in  cyanide  solutions  is  determined  by 
measuring  the  volume  of  the  gases  expelled  from  the 
solution  on  boiling,  absorbing  the  oxygen  by  alkaline 
pyrogallate  solution,  and  measuring  the  residual  ni- 
trogen ;  the  weight  of  the  oxygen  is  obtained  by  meas- 
uring in  a  Japp  gravi-volumeter  a  quantity  of  air  cor- 
responding to  the  volume  of  oxygen  found.  To  re- 
ceive the  gases  expelled  from  the  boiling  solution  a 
Lunge  nitrometer  may  be  used,  to  the  side  tube  of 
which  a  flask  completely  rilled  with  the  cyanide  solu- 
tion is  connected  by  a  piece  of  capillary  tubing,  also 
rilled  with  the  solution,  the  pyrogallate  being  intro- 
duced through  the  funnel  after  disconnecting  the  flask. 
Or  else  a  Rammelsburg  burette  filled  with  water  free 
from  air  may  be  used  to  receive  the  gases,  the  side 
tube  of  the  burette  being  connected  to  a  vessel  con- 
taining water,  whilst  the  upper  end  is  joined,  after 
the  gases  have  been  expelled  from  the  cyanide  solu- 
tion, to  a  U-shaped  tube  containing  the  pyrogallate 
solution ;  the  mixed  gases  are  forced  to  enter  this 
tube  repeatedly  by  raising  and  lowering  the  water  res- 
ervoir. The  boiling  of  the  cyanide  solution  must  in 
this  case  be  continued  until  the  water  in  the  burette 


*  A.   Prister.      Journal  of   the   Chemical   and   Metallurg- 
ical Society  of  South  Africa. 


MILL   AND    SMELTER    METHODS.       91 

becomes  warm,  when  it  may  be  assumed  that  any 
gases  dissolved  by  it  have  been  again  expelled.  Not 
less  than  300  cc.  of  the  solution  should  be  taken  for 
each  test.  Either  modification  of  the  method  is  said 
to  give  good  results. 

Specimen  Analysis  of  Mill  Solutions. 

The  exact  composition  of  mill  solutions  is,  of 
course,  constantly  changing  with  the  nature  of  the 
ores  treated,  or  through  other  causes,  but  on  the  whole, 
after  it  has  taken  up  'its  zinc  and  formed  the  decom- 
position products,  the  solution,  when  properly  looked 
after,  does  not  change  materially.  This  is  to  be  ex- 
pected, as  while  apparently  the  same  solution  is  used 
over  and  over,  this  is  not  strictly  so.  Part  of  the  solu- 
tion is  lost  in  every  charge  worked,  zinc  is  pptd.  in 
every  charge  of  ore  and  other  reactions  take  place,  so 
that,  broadly  speaking,  the  solution  is  continually 
changing  through  chemical  reactions,  is  being  wasted 
and  lost  in  one  end  of  the  process  and  added  to  and 
made  up  in  the  other.  The  following  specimen  analy- 
sis of  the  solutions  in  use  at  the  works  of  the  Metallic 
Extraction  Company  show  great  uniformity  even 
after  years  of  use. 

Starting  in  with  a  pure  solution  of  potassium  cya- 
nide, (a)  shows  its  composition  after  one-half  year's 
use,  (b)  after  two  and  one-half  year's  use,  and  (c) 
after  six  vears'  use.  The  same  amount  of  variation 


92       MILL   AND    SMELTER    METHODS. 

could  easily  have  been  found  in  an  examination  of  the 
analysis  for  the  first  six  months. 

(a)  %  '(b)  %  (c)  % 

KCN   0.455  o-53°°  0-380 

HCN  0.058  0.0269  0.060 

K4Fe(CN)c 0.095  0.0580  0.036 

KCNS 0.023  0.0388  0.050 

ZN 0.338  0.3340  0.374 

Ca  0.085  0.1560  0.176 

Alkalinity    0.560  0.5400  0.720 

Total  solids  in  solution i  .970  1 .9020  1 .962 


MILL    AND    SMELTER    METHODS.       93 


CHAPTER  VIII. 


Ore   Testing    by   the  Cyanide   Process. 


A  very  important  part  of  the  duties  of  the  chem- 
ist in  a  cyanide  works  is  to  make  extraction  and  con- 
sumption tests  on  the  ores  received.  It  is  not  unusual, 
in  large  custom  works,  to  make  such  tests  on  each'  lot 
of  ore  received.  But  of  greater  importance,  perhaps, 
is  the  testing  and  examination  of  ores  for  the  pur- 
pose of  determining  their  adaptibility  to  cyanide 
treatment. 

Preliminary  Tests. 

A  physical  examination  of  the  ore  will  give  a  good 
idea  of  the  screen  aperture  through  which  it  must  be 
passed  in  order  to  obtain  a  good  extraction.  For  ex- 
ample, if  the  ore  is  a  porous  or  cellular  oxidized -pro- 
duct, perhaps,  crushing  through  a  0.44"  screen  aper- 
ture will  suffice;  if  of  dense  and  solid  structure  it 
'should  be  crushed  to  pass  screen  apertures  varying 
from  0.024  to  0.018  inch.  Flinty  material,  pyritic  and 
telluric,  silver  ores,  etc.,  may  have  to  be  reduced  to 
impalpable  powder  to  obtain  the  desired  extraction. 

Roasting,  apart  from  oxidizing  or  driving  off  the 
volatile  metals,  also  resembles  fine  crushing  in  that  it 
makes  the  ore  porous,  allowing  the  solutions  to  pene- 
trate between  the  individual  ore  particles,  much  as  if 


94       MILL   AND    SMELTER    METHODS. 

they  had  been  reduced  to  a  very  fine  state  of  division. 
Consumption  Test. 

These  are  best  made  with  direct  cyanide  solutions, 
and,  as  lime  is  invariably  used  to  correct  acidity,  add 
it  at  once  and  note  results.  Weight  up  4  separate  A. 
T.'s  of  the  crushed  ore  and  place  in  250  cc.  glass 
stoppered  bottles  ;  add  fresh  slacked,  pure  lime,  at  the 
rate  of  5,  10,  15  and  20  Ibs.  to  the  ton  of  ore  and  then 
30  cc.  of  cyanide  solution  to  each  bottle;  place  on  the 
agitator  for  30  minutes;  filter  and  determine  cyanide 
consumption. 

The  lowest  consumption  may  be  found  with  10  Ibs. 
of  lime  (excess  of  lime  will  itself  consume  cyanide)* 
-indicating  that  about  10  Ibs.  of  lime  should  be  used  per 
ton  of  ore. 

If  a  high  consumption  of  cyanide  is  shown  when 
15  to  20  Ibs.  of  lime  are  added,  see  if  soluble  cyanides 
can  be  removed  by  preliminary  water  washes  (use 
three  washes,  each  double  the  volume  of  the  ore). 

Should  the  cyanide  consumption  remain  high  after 
water  washing,  look  out  for  oxidized  copper  com- 
pounds, and,  if  their  presence  is  proven,  treat  the  ore 
first  to  three  washes  of  5%  sulphuric  acid,  followed  by 
an  alkaline  wash  (sodium  hydrate  preferably). 


*  The  consumption  of  cyanide  in  laboratory  tests  when 
pure  solutions  are  used  is  usually  25%  higher  than  mill 
results  with  zinciferous  solutions.  —  (P.  Argall,  Min.  Indus- 
try, Vol.  VI.,  page  373.) 

•> 


MILL   AND    SMELTER    METHODS.       95 

Organic  compounds  are  often  rendered  harmless 
by  a  preliminary  treatment  with  sulphuric  acid. 

If  the  acid  wash  fails,  try  concentrating  out  the 
heavy  minerals  previous  to  cyaniding.  Copper,  anti- 
money,  lead  and  other  sulphides  are  thus  removed,  and 
the  tailings  are  invariably  rendered  amenable  to  cya- 
nide treatment. 

_  A 

Preliminary  Extraction  Tests. 

These  are  preferably  made  in  the  glass  stoppered 
bottles  used  for  the  cyanide  consumption  tests.  Should 
the  ore  under  investigation  be  a  gold  ore,  containing 
no  appreciable  amount  of  silver,  weigh  up  loj  A.  T.'s 
of  the  puverized  ore,  add  the  amount  of  lime  found 
necessary  to  neutralize  acidity,  and  place  in  the  glass 
stoppered  bottles.  Make  up  the  following  solutions 
of  cyanide  from  the  stock  bottle : 

0.300% — Put  30  cc.  in  each  of  two  bottles.  Dupli- 
cate tests. 

0.200% — Put  30  cc.  in  each  of  two  bottles.  Dupli- 
cate tests. 

0.100% — Put  30  cc.  in  each  of  two  bottles.  Dupli- 
cate tests. 

0.050% — Put  30  cc.  in  each  of  two  bottles.  Dupli- 
cate tests. 

0.025% — Put  30  cc.  in  each  of  two  bottles.  Dupli- 
cate tests. 

Place  on  agitator  for  eight  hours.  Allow  to  stand 
for  four  hours,  so  far  as  one  set  of  bottles  are  con- 
cerned, allowing  the  duplicates  to  remain  on  the  agi- 


96       MILL   AND    SMELTER    METHODS. 

tator  sixteen  hours.  Remove,  decant  on  to  dry  filter 
paper,  take  up  10  cc.  of  the  filtrate  and  titrate  for 
cyanide  consumption.  Now  wash  out  the  bottles  and 
give  two  water  washes  on  the  filter,  dry  and  assay  the 
residue  for  gold  in  the  usual  manner. 

From  these  tests  the  following  are  deduced : 

(1)  The  proper  strength  of  the  solution  to  attain 
the  best  results  on  the  ore. 

(2)  The  time  required  for  agitation,  eight,   six- 
teen or  more  hours. 

(3)  The  cyanide  consumption. 

These  tests  are  quickly  and  cheaply  made,  and  can 
be  repeated  or  modified  and  concordant  results  ob- 
tained, results  which  are  satisfactory  to  competent 
cyanide  experts. 

It  has  been  found  that,  for  silver  ores,  solutions 
from  0.25%  to  0.75%  are  necessary  to  attack  the  sul- 
phides, hence  the  following  solution  strengths  are  rec- 
ommended for  silver  or  for  gold-silver  ores:  0.25%, 
0.30%,  0.40%,  0.50%,  0.75%. 

The  lime  found  necessary  in  bottle  tests  to  neutral- 
ize the  acidity  is  about  35%  more  than  is  required  on 
a  full  working  scale.  Mass  action  in  the  latter  case 
probably  accounts  for  this. 

Should  the  extraction  on  all  the  series  of  bottles 
be  low,  put  on  another  series,  using  the  percentage 
of  cyanide  that  promised  the  better  results  in  the 
previous  case,  but  have  the  ore  reduced  to  different 
degrees  of  fineness,  say  to  pass  a  screen  aperture  of 


MILL   AND    SMELTER    METHODS.       97 

o.on"  — About  40  apertures  to  the  inch. 
0.0087" — About  50  apertures  to  the  inch. 
0.0055" — About  100  apertures  to  the  inch. 
0.0030" — About  150  apertures  to  the  inch. 
0.0025" — About  200  apertures  to  the  inch. 

These  would  show  the  increased  extraction  due  to 
fine  grinding,*  and,  should  the  extraction  remain  un- 
satisfactory, add,  after  two  hours'  agitation,  in  a  new 
series  of  bottles,  0.15%  to  0.25%  of  the  weight  of  the 
cyanide  present  in  'solution,  of  cyanogen-bromide. 
This  salt  will  often  give  good  gold  extraction-  on 
heavy  sulphides  or  medium-grade  gold  telluride  ores, 
particularly  when  the  ore  is  ground  fine.  Moreover, 
by  the  use  of  cyanogen-bromide,  the  cost  of  roasting 
may  be  avoided,  and  it  then  becomes  necessary  to 
compare  the  cost  of  fine  grinding  plus  -bromo  cyanide 
with  that  of  roasting. 

The  bromo  cyanogen  is  best  added  at  intervals  of 
two  or  more  hours,  as  its  action  is  rapid  and  is  not 
maintained  for  any  considerable  time.  If,  for  exam- 
ple, the  agitation  test  is  to  be  for  a  period  of  eight 
hours,  the  bromo  is  best  added  at  two  hours,  four 
hours  and  six  hours  from  the  starting  of  the  test ;  the 
bromo  cyanogen  acts  as  a  cyanogen  liberator,  displac- 


*  The  finer  the  ore  is  ground,  the  easier  and  quicker 
the  silver  sulphides  are  attacked  by  weak  solutions.  Com- 
mercial results  will  thus  lie  between  fine  grinding  anfl  high 
cyanide  consumption,  for,  the  weaker  the  solution  the 
lower  the  cyanide  consumption. 


98       MILL   AND    SMELTER    METHODS. 

ing  one  molecule  of  cyanogen  from  the  KCN  present 
and  at  the  same  time  giving-  off  its  own  cyanogen 
thus : 

KCN+Au+KCN      ( 

Br  CN+Au+KCN    j  = 

Potassium  cyanide  has  practically  no  action  on 
gold  tellurides,  but  the  cyanogen  liberated  in  the 
nascent  state  in  the  cyanide  solutions,  by  the  addition 
of  bromo  cyanogen,  acts  as  a  powerful  solvent,  both 
of  the  gold  and  the  tellurium,  provided  the  ore  is  in 
the  finest  possible  state  of  division.  It  will  be  noted 
that  oxygen  is  not  required  in  the  above  reaction,  and. 
unlike  agitation  tests  with  plain  cyanide,  the  bottles 
can  be  filled  with  ore  and  solution,  or  very  nearly  so, 
whereas  with  cyanide  only,  ample  air  space  should  be 
left  in  the  bottles  and  the  stoppers  removed  once  or 
twice  during  the  agitation  and  the  air  renewed. 

Bromo- cyanogen  is  a  very  difficult  substance  to 
obtain  in  the  West,  but,  in  reference  to  its  use  in  West 
Australia,  Mr.  Alfred  James  states:*  ''It  is  now  usu- 
ally made  on  the  spot,  from  imported  bromo-salts,  in 
view  of  the  difficulty  of  getting  the  steamship  com- 
panies to  carry  the  actual  bromo-cyanide  crystals. 
The  method  of  preparation  is  as  follows :  Bromo  salts 
include  potassium  bromide  and  bromate,  roughly  in 
quantities  required  for  the  reaction.  Assuming  this 
to  be  2KBr+KBrO3  +  3KCN  +  3H2SO4=3BrCN  + 


Engineering  and   Mining  Journal,  Jan.  7,  1904. 


MILL   AND    SMELTER    METHODS.       99 

3  K2S04  +  3H20.     238  +  167  +  195  +  294  —  318  + 
522  +  54- 

"Bromo  salts  imported  from  Germany  are  very 
impure,  but  contain  the  correct  mixture  to  satisfy  the 
above  reaction.  The  charge  used  at  Kalgoorlie  to  gen- 
erate 100  pounds  of  BrCN  is : 

Mixed  bromo  salts 125  Ibs. 

Cyanide  ( 100% )  65  Ibs. 

Sulphuric  acid  (70%) 147  Ibs. 

"The  salts  are  agitated  in  a  wood  or  lead  lined  vat 
of  about  200  gallons'  capacity,  securely  covered  by  a 
lid,  through  which  a  revolving  stirrer  or  paddle  works. 
Above  this  is  a  small  vat,  in  which  is  stored  the  neces- 
sary charge  of  cyanide  dissolved  in  forty  gallons  of 
water.  The  vat  is  first  three-fourths  filled  with  water, 
the  agitator  started,  and  the  sulphuric  acid  added 
slowly  and  carefully.  The  whole  charge  is  now  left 
to  stand  until  cool,  say  one  hour,  as  the  great  heat 
generated  by  the  addition  of  the  acid  would  destroy 
the  bromo-cyanide.  When  cool,  the  mixed  bromo- 
salts  are  added  gradually  and  the  solution  of  cyanide 
run  in  simultaneously  with  constant  stirring.  The  re- 
action commences  almost  immediately,  but  is  not  thor- 
oughly completed  until  after  six  hours'  continuous 
agitation." 

This  method  can  be  modified  for  laboratory  use 
where  the  bromo-salts  are  not  available,  as,  for  exam- 
ple, following  the  equation  given  above,  we  may  pro- 
ceed as  follows: 


ioo     MILL   AND    SMELTER    METHODS. 

Weigh  up  25  grams  of  potassium  bromate  and 
35-5  grams  of  potassium  bromide  and  dissolve  them 
in  about  400  ce.  of  cold  water.  (Solution  A.) 

Weigh  up  29.25  grams  of  potassium  cyanide  and 
dissolve  in  200  cc.  of  water.  (Solution  B.) 

Dilute  44  grams  of  sulphuric  acid  to  400  cc.  and 
cool  thoroughly.  (Solution  C.)  The  strength  of  the 
sulphuric  acid  should  be  determined  with  an  N-io  so- 
lution of  sodium  hydrate,  I  cc.  of  which  is  equivalent 
to  .0049  grams  sulphuric  acid. 

Place  solution  (C)  in  a  large  flask  when  quite 
cool,  place  a  funnel  in  neck  and  pour  in  solutions 
(A  and  B)  simultaneously  and  in  very  small  streams, 
allowing  them  to  mix  in  the  funnel  and  drop  into  the 
acid  solution  in  the  large  bottle.  Finally  agitate  the 
mixture  for  six  hours,  When  the  reaction  should  be 
complete  and  the  solution  ready  for  use.  This  solu- 
tion should  titrate  about  4.5%  bromo  cyanogen  (4.7% 
theoretically).  If  the  reactions  are  completed  the  solu- 
tion should  be  neutral  to  methly  orange  and  phe- 
nolpthalein ;  should  it  be  acid,  however,  it  must  be 
carefully  neutralized  by  an  N-io  potassium  or  sodium 
hydrate  solution,  as  alkali  decomposes  bromo  cyano- 
gen care  must  be  used  to  avoid  any  excess.  Bromo 
cyanogen  made  in  this  way  will,  according  to  Fulton,* 
keep  several  months  in  a  tight  stoppered  bottle. 

For  accurate  tests  or  delicate  research  work,  pure 


*  Bulletin   No.    1  of  the   South  Dakota  School  of  Mines, 
which  see  for  fuller  details,  if  required. 


MILL   AND    SMELTER    METHODS.      101 

crystals  of  bromo  cyanogen  can  be  made  from  bromine 
and  mercuric  cyanide,  as  follows:  When  one  part  of 
liquid  bromine  is  allowed  to  flow  gradually  on  2  parts 
of  mercuric  cyanide  (dry  salt)  in  a  retort  t  surrounded 
by  ice,  bromo  cyanogen  and  mercuride  bromine  are 
formed  with  great  evolution  of  heat. 

Bromo  cyanogen  sublimes  in  needles,  contaminated 
with  free  bromine,  which,  however,  flows  back  into  the 
retort  and  enters  into  complete  combination.  Gentle 
heat,  by  means  of  an  alcohol  lamp,  is  then  applied  and 
the  Br  CX  sublimed  into  a  receiver  surrounded  by  ice 
water.  Bromo  cyanogen  crystals  obtained  in  this  way 
can  be  kept  in  a  tightly-corked  bottle  in  a  cold  place 
for  use  indefinitely. 

Roasting. 

Should  none  of  the  foreging  tests  give  satisfactory 
results  the  ore  may  be  roasted  in  the  muffle,  first  to 
a  dead  roast ;  second,  in  case  of  silver  ores,  by  a  chlo- 
ridizing  roast,  as  plain  roasting  invariably  interferes 
very  seriously  with  silver  extraction,  and  almost  as 
persistingly  greatly  increases  the  extraction  of  the 
gold. 

In  a  chloridizing  roast  the  loss  of  gold  by  volatili- 
zation is  often  very  heavy,  and  should,  in  all  cases, 
be  determined  in  the  following  manner : 


f  The  apparatus  for  this  work  is  best  a  small  retort 
and  receiver,  the  retort  having  an  opening  for  a  small 
thistle  tube  with  stop  cork  for  the  introduction  of  bro- 
mine. 


102    .MILL   AND    SMELTER    METHODS. 

Mix  the  necessary  amount  of  dry  salt  with  the  ore, 
and  reduce  to  pass  the  desired  screen  aperture.  As- 
say for  gold  and  silver,  then  weigh  up  50  to  100  grams 
of  the  mixed  ore  and  salt,  place  in  a  roasting  dish 
and  set  in  a  cool  muffle.*  Gradually  raise  the  temper- 
ature to  cherry-red.  When  the  fumes  cease  coming 
off,  remove,  cool  and  weigh.  Note  the  loss  of  weight, 
then  assay  for  gold  and  silver  and  calculate  the  loss 
of  precious  metals. 

In  practice  the  salt  is  often  added  toward  the  end 
of  the  roasting  furnaces  to  prevent  gold  losses  in  the 
earlier  stages  of  roasting.  Chloridizing  roasting  is 
only  necessary  for  silver  ores,  and  where  the  amount 
of  the  silver  is  considerable,  it  may  be  preferable  to 
leach  the  roasted  ore  first  with  sodium  thiosulphate  to 
remove  the  silver  chloride ;  wash  well,  and  extract  the 
residue  of  the  gold  and  some  of  the  silver  compounds 
by  cyanide  solutions.  Except  for  the  fact  that  gold  is 
soluble  in  thiosulphate  solutions,  a  combination  of  the 
former,  with  the  cyanide  process,  could  be  used  on 
chlorodized  ores ;  the  former  to  remove  the  silver,  the 
latter  the  gold.  I  have  found  that  thiosulphate  would 
extract  in  some  cases  50%  of  the  gold  present  in  chlori- 


*  Chloridizing  roasts  must  be  started  at  a  very  low 
temperature  and  gradually  raised  to  cherry-red  at  the  end, 
moreover,  when  the  sulphur  exceeds  4%,  a  preliminary 
roast  is  desirable,  then  cool,  add  the  salt  and  complete  the 
roast.  Gold  is  easily  volatilized  as  chloride,  but  is,  to  a 
large  extent,  recoverable  from  the  dust  collected  in  a 
proper  system  of  condensing  flues. 


MILL   AND    SMELTER    METHODS.      103 

dized  ores,  while  subsequent  cyanide  treatment  ex- 
tracted not  only  a  large  proportion  of  the  remaining 
gold,  but  also,  in  cases,  as  much  as  10%  of  the  remain- 
ing silver  values.  The  Patera  process  is  cheaper  than 
cyanide  in  the  treatment  of  these  ores,  but  it  never 
gives  a  satisfactory  gold  extraction.  Therefore,  when 
the  cyanicides  can  be  removed  by  preliminary  water 
washes,  followed  by  an  alkaline  wash,  the  cyanide 
process  will  extract  both  the  gold  and  silver  in  one 
operation,  greatly  shortening  and  simplifying  the 
treatment  of  the  ore.  In  testing  ores,  as  above  out- 
lined, the  chemist  should  clearly  keep  in  mind  that 
the  solution  of  his  problem  is,  that  process  or  combi- 
nation of  processes  that  will  give  the  highest  results 
at  the  least  expense  of  operation,  and,  if  possible,  the 
the  smallest  investment  of  capital  in  a  plant. 

Modification  of  Bottle  Test. 

In  the  foregoing  tests  it  is  assumed  the  ore  treated 
in  the  bottles  is  fine  enough  for  assaying.  Should 
this  not  be  the  case,  the  extraction  can  be  determined 
by  assaying  the  solutions  by  the  evaporation,  or  the 
Argall  method  (see  page  67).  The  solutions  from  one 
bottle  would  be  used  for  determining  cyanide  con- 
sumption, the  duplicate  being  used  for  this  assay. 
Apart  from  this  it  is  always  advisable  to  test  an  occa- 
sional solution  assay  against  the  corresponding  tailing 
assay,  the  one  giving  the  precious  metal  extraction, 
the  other  the  amount  remaining  in  the  tailings,  and 


104     MILL   AND    SMELTER    METHODS. 

they  should  check  within  the  limits  of  experimental 
error. 

If  the  ore  experimented  with  is  to  be  treated  by 
agitation,  the  bottle  tests  give  all  the  information  re- 
quired, if,  by  percolation,  it  is  necessary  to  establish 
the  ratio  of  time  between  agitation  and  percolation. 
It  is,  of  course,  variable,  but  approximates  i  for  agita- 
tion to  4  for  percolation. 

Percolation    l^ests. 

These  can  be  made  in  glass  percolators  holding 
about  four  pounds  of  ore.  The  ore,  in  which  is  thor- 
oughly incorporated  the  required  amount  of  lime, 
should  be  placed  evenly  and  carefully  in  the  percola- 
tor, gently  pressed  around  the  sides  to  prevent  chan- 
neling, and  the  solution  added  on  top.  The  strength 
of  the  solution  to  be  used  has  been  previously  deter- 
mined from  the  results  of  the  bottle  tests. 

Allow  the  solution  to  stand  on  the  ore  four  hours, 
then  allow  to  percolate  through.  Allow  the  ore  to 
drain  dry  every  day ;  after  the  second  day's  treatment, 
turn  the  ore  out  from  the  percolator  when  drained 
dry,  and  cut  out  a  sample  for  assay,  to  show  the  ex- 
traction, and  return  the  remainder  to  the  percolator. 
Keep  up  this  sampling,  daily,  until  the  final  extrac- 
tion is  reached,  so  far  as  one  percolator  is  concerned. 
Allow  the  duplicate  to  run  on  without  being  disturbed, 
but  it  must  be  drained  dry  daily. 

The  percolator  tests  should  follow  the  usual  cya- 
nide practice : 


MILL   AND    SMELTER    METHODS.      105 

1.  Water,  or  alkaline  wash,  if  required. 

2.  Weak  solution. 

3.  Strong  solution. 
4  Weak  solution. 

5.     Water  wash.     Finish. 

If  the  preliminary  wash  is  unnecessary,  add  at 
once  the  strong  solution,  followed  by  No.  4  and  No.  5. 

When  copper  or  organic  compounds  are  present, 
or  to  obtain  details  of  change  in  the  solutions,  sev- 
eral small-sized  working  tests  may  be  made  in  wooden 
or  steel  vats,  holding  1,000  or  2.000  pounds  of  ore. 
Proceed  as  with  the  percolators,  but  allow  the  solution 
to  pass  through  filiform  zinc  in  two  or  more  glass  or 
porcelain  cells.  Note  the  precipitation  and  analyze 
the  solutions  on  completion  of  the  tests.  Be  careful 
that  the  solutions  are  aerated  before  returning  them  to 
the  leaching  vats,  for,  as  the  solutions  in  percolating 
through  a  charge  of  ore  are  gradually  deprived  of  their 
oxygen,  it  is  found  that  the  lowest  layers  of  ore,  those 
nearest  the  filter,  do  not  extract  as  well  as  those  layers 
above.  This  can  be  remedied  by  running  on  an  occa- 
sional aerated  solution  from  below.  This  must  be  per- 
formed slowly,  to  avoid  forming  holes  or  channels  in 
the  charge.  In  this  way  solutions  rich  in  oxygen  are 
brought  in  contact  with  the  bottom  portions  of  the 
charge,  and  a  more  even  extraction  thus  obtained. 


io6     MILL   AND    SMELTER    METHODS 


CHAPTER   IX. 


The  Analysis  of    Bronzes  and    Bearing   Metals. 

By  I-I.  E.  Walters  and  O.  I.  Affelder.* 


Bronzes. 

Weigh  I  gram  of  the  sample  (-J  gram  if  the  lead 
is  over  15%)  into  a  No.  2  beaker,  cover  with  a  watch- 
glass,  add  10  cc.  nitric  acid  (Sp.  Gr.  1.42)  and  warm 
until  all  is  dissolved.  When  in  solution,  add  40  cc. 
hot  water  and  boil  five  minutes,  filter,  wash  with  a  2% 
nitric  acid  solution,  burn  and  weigh  as  SnCX.  To  the 
filtrate  add  25  cc.  strong  ammonia  and  heat  to  boiling, 
then  add  about  5  grams  ammonium  per-sulphate  and 
boil  from  five  to  ten  minutes.  Make  acid  with  sul- 
phuric acid,  filter  and  wash  with  hot  water.  The  lead 
will  remain  on  the  filter  as  lead  peroxide.  Transfer 
the  precipitate  and  lead  to  a  beaker  in  which  the  pre- 
cipitation was  made,  add  water  and  stir  well  to  disin- 
tegrate the  filter  paper.  Dilute  to  600  to  700  cc.  with 
cold  water,  add  about  3  grams  potassium  iodide  and 
some  starch  solution.  When  all  the  iodide  is  dissolved, 
add  10  cc.  hydrochloric  acid,  stir  well  and  titrate  with 
1/20  normal  solution  sodium  thio-sulphafe  until  the 
solution  changes  from  the  dirty  and  dark  yellow  solit- 

*  Journal    American    Chemical    Society,   June,    1903. 


MILL   AND    SMELTER    METHODS.      107 

tion  to  a  bright  lemon  yellow ;  or  an  excess  of  sodium 
thio-sulphate  may  be  added  and  the  excess  titrated 
with  1/20  normal  iodide  solution  until  the  color 
changes  from  the  bright  yellow  of  the  lead  iodide 
present  to  the  dirty  and  dark  yellow.  The  number 
of  cc.  of  sodium  thio-sulphate  used,  multiplied  by 
0.5175,  will  give  the  percentage  of  lead.  Where  speed 
is  not  desirable  the  lead  may  be  determined  by  adding 
sulphuric  acid  to  the  filtrate  from  the  oxide  of  tin,  or 
the  lead  and  copper  may  be  deposited  with  the  elec- 
tric current. 

Dilute  the  filtrate  from  the  lead  peroxide  to  500 
cc.,  heat  to  boiling  and  add  50  cc.  of  a  20%  sodium 
thio-sulphate  solution,  boil  five  minutes,  filter,  wash 
with  hot  water,  burn  and  weigh  as  CuO. 

Copper  may  also  be  determined  as  in  the  following 
method,  which  is  a  modification  of  Low's  method : 
Dissolve  £  gram  of  the  sample  in  10  cc.  nitric  acid. 
When  in  solution,  dilute  with  cold  water  and  add  so- 
dium carbonate  until  the  solution  is  alkaline,  make 
acid  with  acetic  acid  and  add  about  3  grams  potassium 
iodide  and  some  starch  solution.  Titrate  with  a  so- 
dium thio-sulphate  solution  which  has  been  standard- 
ized with  pure  copper. 

Oxidize  the  filtrate  from  the  copper  sulphide 
thrown  down  by  the  thio-sulphate  as  described  above, 
with  nitric  acid  and  potassium  chlorate  and  evaporate 
until  the  volume  is  about  300  cc.  Make  a  basic  acetate 
separation  and  determine  iron  or  aluminum  by  the 


io8     MILL   AND   SMELTER    METHODS. 

well-known  methods.  Make  the  filtrate  from  the  iron 
or  alumina  strongly  alkaline  with  ammonia,  heat  to 
boiling  and  add  ammonium  per-sulphate,  boil  five 
minutes,  filter,  and  wash  with  hot  water,  burn,  and 
weigh  as  Mn..O4. 

To  the  filtrate  from  the  manganese  add  ammonium 
phosphate  in  excess, .heat  to  boiling,  and  add  hydro- 
chloric acid  until  there  is  but  a  slight  excess  of  am- 
monia, boil  five  minutes,  filter,  and  wash  with  hot 
water.  The  ppt.  may  be  dried  and  weighed  as 
ZnNH4PO4,  or  it  may  be  filtered  on  a  Gooch 'crucible 
and  ignited  to  Zn2P2O7.  It  may  also  be  titrated  with  a 
standard  acid  and  alkali. 

Any  nickel  which  may  be  present  will  be  found 
in  the  filtrate  from  the  zinc,  and  may  be  pptd.  as 
sulphide  and  ignited  to  NiO. 

If  manganese  is  present  in  small  quantities,  it  may 
be  determined  in  a  separate  portion  by  the  following 
method:  Weigh  0.2  gram  of  the  sample  into  a  suit- 
able test  tube,  add  10  cc.  nitric  acid  (Sp.  Gr.  1.20),  and 
warm  until  the  sample  is  dissolved  and  all  nitrous 
fumes  are  driven  off.  Add  15  cc.  silver  nitrate  solu- 
tion (1.33  grams  of  the  salt  to  I  litre  of  water)  and 
about  -J  gram  of  ammonium  per-sulphate,  warm  until 
the  manganese  is  oxidized  to  permanganic  acid,  cool, 
transfer  to  a  beaker,  dilute  to  100  cc.  and  titrate  with 
standard  sodium  arsenite  or  hydrogen  peroxide  until 
disappearance  of  the  pink  color. 


MILL   AND    SMELTER    METHODS.      109 

Determination  of  Phosphorus. 

To  determine  phosphorus,  dissolve  I  gram  of  the 
sample  in  5  cc.  fuming  nitric  acid,  evaporate  to  expel 
most  of  the  free  acid,  add  10  cc.  cone.  HC1  and  water, 
heat  to  boiling  and  ppt.  the  lead,  tin  and  copper  with 
metallic  zinc,  filter  and  wash  with  hot  water.  To  the 
filtrate  add  some  iron  solution  free  from  phosphorus 
and  10  cc.  HNO3,  boil  a  few  minutes,  and  then  ppt. 
with  ammonia  and  filter  to  separate  most  of  the  zinc, 
dissolve  the  ppt.  in  hot  HNO3  and  ppt.  the  phosphorus 
with  molybdate  solution.  The  yellow  ppt.  may  be 
weighed  or  titrated. 

Bearing  Metals. 

If  the  sample  is  high  in  tin  and  low  in  lead,  pro- 
ceed as  outlined  for  bronzes ;  but  if  the  sample  is  high 
in  lead  and  contains  antimony,  proceed  as  suggested 
by  Mr.  George  Hopkins,  chemist  to  the  Carrie  fur- 
naces of  the  Homestead  Steel  Works,  he  having  found 
that  the  addition  of  an  excess  of  pure  tin  will  insure 
the  complete  separation  of  the  antimony  with  the 
oxide  of  tin.  Weigh  0.5  gram  of  the  sample  and  J 
gram  of  pure  tin  into  a  tall  No.  2  beaker,  cover  with 
a  watch-glass,  add  20  cc.  HNO3  (Sp.  Gr.  1.33)  and  boil 
down  to  a  pastiness,  add  40  cc.  hot  H..O  and  boil  a  few 
minutes,  filter  and  wash  with  a  2%  HNO3,  burn  an.1 
weigh  as  SnO,+Sb2O4.  The  filtrate  is  made  strongly 
alkaline  with  caustic  potash  and  the  lead  oxidized  by 
adding  about  10  grams  ammonium  per-sulphate.  Tl.c 


no     MILL   AND    SMELTER    METHODS. 

rest  of  the  analysis  is  carried  out  as  outlined  for 
bronzes. 

To  determine  the  antimony,  weigh  i  gram  of  the 
sample  and  i  gram  KI  into  a  No.  2  beaker,  add  80  cc. 
HC1,  (Sp.  Gr.  i.io)  and  boil  gently  for  one  hour,  filter 
on  a  weighed  paper  of  Gooch  crucible  and  wash  with 
dilute  HC1,  and  then  with  hot  H,O  until  free  from 
chlorides.  Wash  once  with  alcohol,  dry  for  one  hour 
at  ioo°C.  and  weigh.  The  increase  in  weight  is  me- 
tallic antimony.  Calculate  this  to  SbL,O4  and  subtract 
from  the  weight  of  the  stannic  mixed  oxides ;  calcu- 
late the  tin  from  the  weight  of  the  stannic  oxide  found 
and  subtract  the  tin  which  was  added. 

Arsenic  is  determined  in  a  separate  portion  by  any 
of  the  well-known  distillation  methods. 

Bismuth,  if  present,  would  be  found  with  the  cop- 
per sulphide,  and  can  be  determined  by  dissolving  the 
copper  sulphides  in  HNOn  and  ppting.  the  bismuth 
with  ammonia. 


MILL    AND    SMELTER    METHODS,      in 


CHAPTER  X. 


Refinery    Methods. 


Determination  of  Lead  in  Base  Bullion. — The 
most  accurate  method  that  the  author  has  been  able 
to  find  is  due  to  Dr.  Paul  Jannasch  (Praktischer  Leit- 
faden  der  Gewichtsanalyse,  Heidelberg,  1897)..  The 
sample  is  taken  by  means  of  a  punch,  from  one  to  four 
samples  being  taken  from  each  bar  in  the  lot.  These 
samples,  representing  the  whole  lot,  are  melted  in  a 
graphite  crucible  and  poured  into  a  wide,  shallow 
mould.  Such  a  bar  will  represent  a  lot  of  from  one 
to  thirty  or  more  tons  ;  one-half  of  the  bar,  cut  length- 
wise, goes  to  the  shipper,  while  from  the  other  half 
samples  are  cut  with  a  cold  chisel  for  assay.  The 
chemist  is  thus  supplied  with  about  1X3  inches  of  the 
sample,  from  which  he  removes  sufficient  for  his  de- 
termination with  a  file.  Set  the  piece  lengthwise  in  a 
vise  and  first  remove  the  oxidized  outer  surface  with 
the  coarse  file,  then  take  the  part  for  assay. 

To  i  gram  of  the  filings  in  a  3-inch  casserole  add 
5  cc.  nitric  acid  and  3  cc.  water  and  evaporate  to  dry- 
ness.  Be  careful  not  to  oxidize  the  Sb  present  to  SbO2. 
Add  15  cc.  of  water  and  again  evaporate  to  dryness, 
when  the  lead  will  be  seen  to  be  crystallized.  Take 
up  in  dilute  nitric  acid,  boil  and  filter.  Heat  the  fil- 


ii2      MILL   AND    SMELTER    METHODS. 

trate  to  boiling,  and  in  a  test-tube  heat  15  to  20  cc.  of 
a  10%  solution  of  potassium  bichromate.  Add  the  boil- 
ing bichromate  solution  to  the  boiling  nitrate,  grad- 
ually, and  with  constant  stirring.  Now  add  while 
still  warm,,  25  cc.  of  a  I  to  3  mixture  of  water  and 
ammonia,  carefully,  and  with  stirring.  Remove  from 
the  heat  and  allow  to  cool.  When  quite  cold,  filter 
and  wash  with  a  cold  dilute  solution  of  i  part  ammo- 
nia to  25  parts  water.  Dry  the  precipitate  at  100°  C. 
Brush  the  precipitate  out  on  a  piece  of  glazed  paper, 
removing  as  much  as  possible  from  the  filter  paper. 
In  a  weighed  porcelain  crucible  burn  the  filter  paper 
at  a  low  heat,  then  add  the  precipitate  from  the  glazed 
paper,  cover,  and  gradually  raise  the  heat,  by  a  blast 
lamp,  to  a  cherry  red.  After  keeping  at  this  heat  for 
from  fifteen  to  twenty  minutes,  remove  the  crucible, 
cool  in  a  desiccator  and  weigh  as  PbCrO4.  Multiply 
by  64.05  to  obtain  the  percentage  of  lead. 

Knoor  Method   for  Determining  Arsenic   and   Anti- 
mony in  Lead  Bullion,  by  Distillation  in 
the  Knoor  Distilling  Flask. 

Take  \  or  I  gram  of  the  material,  depending  upon 
the  amount  of  As  or  Sb  present — the  greater  the 
amount,  the  less  the  material  taken — but  never  more 
than  i  gram  on  account  of  the  difficulty  of  washing 
thoroughly  a  bulky  precipitate  of  sulphides.  Treat 
directly  in  the  Knoor  flask  with  10  cc.  cone,  sulphuric 
acid  and  take  down  to  dense  fumes.  Allow  the  flask 


MILL   AND   SMELTER    METHODS,      nj 

to  cool.  Add  10  to  15  cc.  water  and  allow  to  cool 
again.  Now  connect  with  the  condenser  and  receiver 
and  add  20  cc.  cone,  hydrochloric  acid.  Commence 
distilling,  adding  through  the  funnel — drop  by  drop 
continually — hydrochloric  acid  stock  solution  made  by 
adding  200  cc.  of  water  to  an  acid  bottle  full  of  C.  P. 
hydrochloric  acid.  The  rate  of  this  addition  should 
not  be  so  great  as  to  greatly  increase  the  bulk  in  the 
flask,  yet  an  excess  of  HC1  must  be  present  to  form  the 
"OUS"  chloride.  The  arsenic  comes  over  in  the  first 
five  minutes,  the  beaker  is  changed  for  another  and  a 
proof  run  for  one  minute  to  be  sure  that  the  As  is  com- 
pletely distilled.  Another  beaker  is  then  substituted 
and  the  distillation  for  antimony  commenced.  The 
heat  is  raised  gradually  until  fumes  show  in  the  con- 
denser. The  density  of  these  fumes  is  the  guide ;  they 
should  not  be  too  dense,  otherwise  the  heat  is  too  great, 
and  should  you  be  working  on  copper  material  the 
cuprous  chloride  would  come  over.  Hydrochloric  acid 
is  now  dropped  in  much  more  slowly,  the  rate  being 
diminished  as  soon  as  the  arsenic  is  distilled.  The  only 
reason  for  adding  HC1' during  the  antimony  determina- 
tion is  that  the  top  of  the  flask  would  become  too  hot 
and  the  solution  "buck"  or  draw  back.  The  antimony 
distills  in  from  40  minutes  to  one  hour,  during  which 
time  the  flask  must  be  protected  from  absolutely  any 
drafts — even  walking  by  quickly  will  cause  a  draft — 
which  will  cause  the  flask  to  cool  off  slightly  and 
"buck." 


114     MILL   AND    SMELTER    METHODS. 

The  arsenious  chloride  and  the  antimonius  chloride 
are  precipitated  with  hydrogen  sulphide,  allowed  to  set- 
tle over  night,  filtered  onto  a  Gooch  crucible,  washed 
with  water,  alcohol,  carbon  sulphide,  alcohol  and 
ether,  in  the  order  named.  This  treatment  is  neces- 
sary, especially  with  antimony,  in  order  to  avoid  high 
results.  In  the  antimony  determinations,  to  the  dis- 
tillate is  first  added  some  tartaric  acid  to  prevent  pre- 
cipitation of  the  antimony  as  oxychloride,  the  distillate 
is  then  neutralized  with  ammonia,  made  just  acid  with 
HC1  and  precipitated  with  hydrogen  sulphide. 

The  arsenic  may  also  be  determined  by  titration 
with  iodine,  using  starch  as  an  indicator. 

The  apparatus  as  shown  (see  cut)  is  supported 
on  an  upright  iron  rod.  Attached  to  the  lower  part  of 
thjs  is  a  ring  and  clamp  supporting  the  water  cooler  hi 
which  is  immersed  the  beakers  for  receiving  the  dis- 
tillate. Above  this  is  a  piece  of  glass  tubing  which 
will  slide  up  or  down  on  the  rod  and  can  be  supported 
at  any  height  by  a  screw  clamp.  The  ring  supporting 
the  flask  and  the  clamps  holding  the  condenser  are 
attached  to  this  tube,  thus  permitting  the  flask  and 
condenser  to  be  raised  at  once,  and-  quickly,  in  the 
event  of  the  distillate  drawing  back  into  the  condenser 
tube.  The  flask  is  set  in  a  disk  of  asbestos  mounted  on 

Note. — The  apparatus  as  designed  by  Mr.  Knoor  is 
manufactured  by  E.  Matchlett  &  Co.,  143  E.  23rd  St., 
New  York  City.  One  set  of  one  condenser  and  three 
flasks  for  $5.00. 


MILL   AND    SMELTER    METHODS.      115 

an  iron  ring  so  that  about  an  inch  of  the  flask  is  below 
the  asbestos.  This  arrangement  keeps  the  top  of  the 
flask  cool  enough  to  permit  of  the  dropping  in  of  HC1 
from  the  funnel.  The  burner  used  must  give  a  hot 
concentrated  flame.  Bumping  of  the  flask  may  occur 
while  taking  down  to  fumes,  and  may  be  prevented  by 
rotating  the  flask. 


box 


Khoor  bifefiHing  Fl* 

^sl^  exnd  CondenAtr. 

Materials  decomposed  by  sulphuric  acid  can  be 
weighed  into  the  flask  direct  and  treated  as  lead  bul- 
lion, save  that  the  reducing  agent  must  be  used.  Cop- 
per bullion  is  dissolved  in  nitric  acid  in  a  beaker,  taken 
down  to  dryness  and  then  evaporated  with  hydro- 
chloric acid  to  expel  all  nitric  acid,  transferred  to  a 


n6     MILL   AND    SMELTER    METHODS. 

flask,  sulphuric  acid  added  and  evaporated  to  approx- 
imately 40  cc.  Connect  up  condenser  and  funnel.  Re- 
duce the  solution  with  'a  10%  solution  of  hypo-phos- 
phorous acid  and  distill.  Samples  containing  much 
silica  must  be  filtered  in  order  to  prevent  bumping  in 
the  flask.  The  amount  of  reducing  agent  .must  be  de- 
termined by  the  change  of  color  in  the  solution  to  a 
light  green,  which  becomes  almost  colorless  when 
down  to  fumes.  An  excess  of  reducing  agent  will 
cause  the  flask  to  boil  over  when  taking  down  to 
fumes. 

The  flow  of  water  through  the  cooler  must  be  just 
sufficient  to  prevent  the  water  becoming  warm. 

The  distinction  between  the  arsenic  and  the  anti- 
mony distillation  is  that  the  arsenic  is  distilled  without 
fumes  showing  in  the  condenser,  while  the  antimony 
distillation  should  just  show  fumes  in  the  condenser 
and  no  more. 

Antimony  in  Hard  Lead. 

After  the  arsenic  has  been  distilled  off,  the  remain- 
ing solution  in  the  flask  is  rinsed  out  with  hot  water, 
add  a  solution  of  sodium  hydroxide  to  slightly  alkaline 
reaction,  then  from  15  to  20  cc.  of  sodium  sulphide 
(made  by  dissolving  I  Ib.  sodium  sulphide  in  i  litre  of 
water),  which  precipitates  the  lead  and  copper  as  sul- 
phides. Allow  to  settle  for  a  few  minutes,  then  filter 
off  the  precipitates  and  wash  them  thoroughly  with 
hot  water, 


MILL   AND    SMELTER    METHODS.      117 

To  the  filtrate,  which  contains  nothing  but  the  anti- 
mony, add  hydrochloric  acid  (i  to  i)  to  slight  acid 
reaction,  stir  thoroughly  and  let  stand  over  night  to 
settle.  Filter  off  the  antimony  sulphide  and  wash 
thoroughly  and  dry  on  the  hot  plate.  When  the  pre- 
cipitate is  dry,  brush  off  the  filter  and  oxidize  the 
paper  in  a  weighed  porcelain  crucible  with  fuming 
nitric  acid,  ignite  and  to  the  crucible  add  the  ppt.  of 
Sb2S3.  Add  a  little  nitric  acid  and  evaporate  several 
times  until  all  the  Sb2S3  is  converted  into  Sb2O4,  ignite 
and  weigh.  The  precipitate  of  Pb  and  Cu  from  the 
sodium  sulphide  can  be  used  in  the  determination  of 
lead,  by  dissolving  in  i  to  i  nitric  acid,  hot,  and  pro- 
ceeding in  the  usual  way. 

The  Knoor  method  will  check  the  above  closely. 

Determination  of  Bismuth  in  Refined  Lead. 

The  quantity  taken  for  analysis  depends  somewhat 
on  the  purity  of  the  lead.  In  ordinary  cases,  where  the 
bismuth  is  about  0.040%  or  over,  50  grams  are  enough  ; 
in  cases  of  greater  purity  the  quantity  should  be  in- 
creased to  100  or  200  grams. 

The  clean  metal  is  rolled  out  as  thin  as  possible  and 
cut  in  pieces  of  5  to  10  grams  each  and  dissolved  in  a 
flask  or  beaker  in  dilute  nitric  acid,  using  for  each 
gram  of  lead  1.2  cc.  of  strong  nitric  acid  (1.42  Sp.  G.) 
diluted  with  3.5  times  its  volume  of  water.  Solution  is 
aided  by  heat  and  evaported  water  being  replaced  from 
time  to  time  to  preserve  the  initial  volume,  the  idea 


n8     MILL   AND    SMELTER   METHODS. 

being  always  to  keep  the  solution  sufficiently  dilute  to 
prevent  the  separation  of  lead  nitrate.  On  this  account, 
too,  no  more  nitric  acid  than  is  necessary  should  be 
used,  as  lead  nitrate  is  much  less  soluble  in  nitric  acid 
than  in  water.  When  solution  is  complete,  precipitate 
with  sulphuric  acid,  adding  enough  to  combine  with  all 
the  lead  and  leaving  about  10  cc.  excess.  Bring  the  so- 
lution and  precipitated  lead  sulphate  to  a  known 
volume,  mix  thoroughly,  allow  to  settle  and  siphon  or 
filter  off  a  measured  amount  of  the  clear  or  nearly 
clear  supernatant  liquid.  This  portion  is  used  for  the 
determination,  the  remaining  liquid  with  the  lead  sul- 
phate being  rejected.  This  procedure  is  to  be  pre- 
ferred to  any  attempt  to  filter  off  and  wash  this, large 
mass  of  lead  sulphate. 

Allowing  for  the  space  occupied  by  the  ppt.,  a 
simple  calculation  will  give  the  amount  of  material 
that  the  solution  to  be  used  actually  represents  (the 
lead  sulphate  from  100  grams  of  lead  occupies  22.5  cc) . 

For  regular  use  in  this  work,  where  determinations 
are  being  made  constantly,  a  set  of  flasks,  one  holding 
810  cc.,  the  other  529  cc.  Flasks  can  easily  be  grad- 
uated with  a  burette,  the  meniscus  being  marked  on  the 
neck  with  a  sharp  file. 

To  start  the  analysis,  75  grams  of  lead  are  dis- 
solved in  a  beaker  in  90  cc.  of  strong  nitric  acid, 
diluted  to  400  cc.  As  soon  as  everything  is  dissolved, 
the  solution  is  transferred  to  the  larger  flask,  in  which 
30  cc.  of  strong  sulphuric  acid,  somewhat  diluted,  ha.s 


MILL   AND    SMELTER    METHODS.      119 

already  been  placed;  the  flask  is  filled  to  the  mark, 
corked  and  well  shaken.  After  allowing  the  ppt.  a  few 
moments  to  subside,  the  liquid  is  filtered  through  a 
dry,  rapid-running  paper  into  the  small  flask,  which  is 
filled  exactly  to  the  mark.  This  whole  operation  is 
performed  so  very  quickly  that  the  slight  change  of 
volume  due  to  cooling  can  be  neglected. 

The  following  calculation  shows  how   much  ma- 
terial the  529  cc.  of  solution  represents : 

Volume  of  liquid  and  ppt 829        cc. 

Volume  of  lead  sulphate  from  75  grams  of 
lead 16.875  cc- 


Actual  volume  of  liquid 793.125  cc. 

Then : 

793.125  :  529  ::  75  : 

x  =  50.02 

or,  in  round  numbers,  50  grams  are  in  actual  use  for 
determination. 

The  solution  from  which  the  bulk  of  the  lead  has 
thus  been  removed  is  at  once  evaporated  in  a  large 
beaker  or  other  suitable  vessel.  When  'jufficiently  con- 
centrated it  is  transferred  to  a  porcelain  dish  or  casser- 
ole of  about  4  inches  diameter,  and  the  evaporatioi. 
continued  until  sulphuric  acid  fumes  come  off  freely. 
It  is  now  removed  from  the  heat  and  as  soon  as  cool 
enough  diluted  with  cold  water  to  about  125  cc.,  then 
boiled  briskly  for  several  minutes  to  insure  the  re- 
solution of  all  the  bismuth  sulphate. 


120     MILL   AND    SMELTER   METHODS. 

After  allowing  the  solution  to  cool  and  settle  for 
two  or  three  minutes,  filter,  washing  the  ppt.  of  lead 
sulphate  with  dilute  sulphuric  acid  (10  cc.  of  acid  to 
I  litre  of  water).  Heat  the  filtrate  nearly  to  the  boil- 
ing point  and  pass  hydrogen  sulphide  gas  through  it 
for  10  to  15  minutes,  allow  to  stand  warm  until  the 
ppted.  sulphides  have  collected  and  settled,  then  filter, 
washing  well  with  hot  water.  When  washed,  without 
removing  the  filter  paper,  return  the  ppt.  to  the  beaker 
in  which  the  precipitation  took  place,  using  as  little 
water  as  possible,  and  then  add  15  to  20  cc.  of  yellow 
alkaline  sulphide.  (The  alkaline  sulphide,  prefereably 
that  of  potassium,  is  best  prepared  from  pure  mater- 
ials by  the  operator ;  the  article  of  commerce  is  seldom 
or  never  pure.)  Heat  to  boiling,  dilute  somewhat, 
allow  to  settle  and  decant  through  the  paper  already 
used  for  filtering  off  the  sulphides.  Repeat  the  treat- 
ment with  a  fresh  portion  of  the  alkaline  sulphides, 
finally  transferring  the  ppt.  to  the  filter  and  washing 
with  water  containing  some  of  the  alkaline  sulphide. 

When  washed,  place  the  filter  and  ppt.  in  the  same 
beaker,  add  5  cc.  of  strong  nitric  acid  diluted  to  25  cc., 
warm  until  the  sulphides  are  dissolved,  and  filter  into  a 
porcelain  dish.  Burn  the  papers  at  a  low  heat,  adding 
the  ash  to  the  solution,  then  add  about  3  cc.  of  sul- 
phuric acid  and  evaporate,  as  before,  to  sulphuric 
acid  fumes.  When  cool,  dilute,  boil,  allow  to  cool  and 
settle,  filter  and  wash  with  dilute  sulphuric  acid.  The 
amount  of  lead  removed  here  is  generally  very  slight ; 


MILL   AND    SMELTER   METHODS.      121 

still,  it  is  not  safe  to  omit  this  evaporation.  To  the 
filtrate  add  a  solution  of  sodium  carbonate  until  the 
solution  is  slightly  alkaline  (a  drop  of  methyl-orange 
is  a  good  indicator  to  use  here)  and  a  few  drops  of  a 
strong  solution  of  potassium  cyanide.  Boil  for  a  few 
minutes  and  allow  to  stand  warm  until  the  ppt.  has 
collected  and  the  supernatant  liquid  is  perfectly  clear; 
this  operation  usually  requires  about  half  an  hour. 
Filter  through  a  moderately  close  filter  paper  and  wash 
with  warm  water.  Dissolve  the  ppt.  from  the  filter  in 
warm  dilute  nitric  acid,  add  ammonia  to  alkalinity  and 
about  3  to  5  cc.  of  ammonium  carbonate  solution.  Heat 
to  the  boiling  point  and  let  it  stand  warm  until  the 
bismuth  carbonate  has  settled  well ;  then,  filter  and 
wash.  Dry  the  paper  and  ppt.  and  remove  the  latter 
as  completely  as  possible,  burning  the  paper  sepa- 
rately. Ignite  in  a  small  porcelain  crucible  at  a  low 
red  heat  and  weigh  as  Bi2O3. 

Bi2O8x.8g65  =  Bi. 

Bismuth  in  Lead  Bullion. 

The  determination  of  bismuth  in  lead  bullion  is 
started  in  the  same  way  as  in  the  method  for  refined 
lead  as  regards  the  quantity  of  material,  solution,  ppt. 
of  the  bulk  of  the  lead  and  the  taking  of  a  measured 
portion  of  the  liquid.  In  this  last  point  the  fact  that 
the  lead  bullion  is  only  about  95%  lead  can  be  taken 
into  account,  if  desired,  though  it  is  rather  a  needless 
refinement.  The  only  difference  in  these  preliminary 


122     MILL   AND    SMELTER   METHODS. 

steps  is,  that  in  the  case  of  bullion,  just  about  enough 
sulphuric  acid  to  combine  with  all  the  lead  is  added, 
instead  of  having  10  cc.  in  excess.  Thus  in  the  case 
cited  under  refined  lead,  where  75  grams  were  taken, 
only  20-22  cc.  of  sulphuric  acid  are  added  instead  of 
30  cc. 

Lead  bullion  does  not  make  a  perfectly  clean  solu- 
tion like  the  refined  lead,  a  considerable  residue  usu- 
ally being  left  after  the  action  of  the  nitric  acid  has 
ceased.  This  residue  is  chiefly  gold  and  antimonial 
compounds  and  in  a  bismuth  determination  can  be 
neglected,  it  being  removed  with  ppted.  lead  sulphate. 

The  measured  portion  of  the  solution,  from  which 
the  bulk  of  the  lead  has  been  removed,  instead  of  being 
at  once  evaporated,  as  in  the  case  of  refined  lead,  is 
made  ammoniacal,  50  cc.  excess  of  ammonia  water 
added  and  hydrogen  sulphide  passed  into  the  hot  liquid 
with  the  formation  of  yellow  ammonium  sulphide.  The 
gas  is  passed  nearly  to  saturation,  then  about  20  cc. 
more  of  ammonia  water  added  and  the  whole  allowed 
to  stand,  warm,  until  the  ppt.  has  completely  subsided. 
The  supernatant  liquid  should  be  clear  yellow  and  the 
ppt.  dark  brown.  By  this  means  a  large  part  of  the 
arsenic  and  antimony  are  kept  in  solution  and  gotten 
rid  of  at  once,  although  some  always  remains  with  the 
ppt.  and  must  be  gotten  rid  of  subsequently.  Filter 
and  wash  slightly.  Place  the  paper  and  ppt.  in  a 
beaker,  add  15  cc.  of  strong  nitric  acid  and  dilute  to 
60  cc,  Warm  until  the  sulphides  are  decomposed  and 


MILL   AND   SMELTER   METHODS.     123 

filter  into  a  four-inch  porcelain  dish.  Burn  the  paper 
and  add  the  ash,  then  10  cc.  of  strong  sulphuric  acid 
and  evaporate  to  dense  fumes.  This  point  corresponds 
with  the  first  evaporation  when  working  on  refined 
lead,  and  with  slight  modifications  the  determination  is 
now  carried  on  exactly  as  in  the  preceding  method.  At 
the  stage  where  the  sulphides  are  treated  with  alkaline 
sulphide,  more  of  the  latter  is  usually  required  than  in 
the  case  of  refined  lead,  owing  to  the  larger  amount  of 
arsenic  and  antimony  to  be  removed — the  quantity  of 
these  remaining  here  being  generally  larger  than  the 
total  amount  in  refined  lead. 

At  the  second  evaporation  it  is  advisable,  on  ac- 
count of  the  quantity  of  silver  and  copper  present,  to 
increase  the  sulphuric  acid  to  5  or  6  cc.  instead  of  3 
cc.  When  precipitating  with  sodium  carbonate  and 
potassium  cyanide,  enough  of  the  latter  must  be  added 
to  bring  all  the  silver,  copper  and  cadmium  into  so- 
lution. 

Notes  on  the  Bismuth  Determination. 

By  the  method  detailed  above,  the  complete  sepa- 
ration of  bismuth  from  arsenic,  antimony,  gold,  silver, 
copper,  cadmium,  lead,  iron  and  zinc  is  readily  and 
perfectly  effected.  The  only  point  to  be  especially 
watched  is  the  removal  of  the  arsenic  and  antimony 
when  working  on  lead  bullion,  and  no  trouble  will  be 
experienced  here  if  the  alkaline  sulphide  is  used  in 
sufficient  quantity.  Preventing  the  loss  of  bismuth,  and 
consequently  low  results,  is,  however,  a  more  difficult 


124     MILL   AND    SMELTER    METHODS. 

matter.  The  following  are  some  of  the  numerous 
ways  in  which  such  loss  can  readily  occur : 

Throughout  the  work  hydrochloric  acid  and  chlor- 
ides must  be  rigidly  excluded.  The  tendency  of  bis- 
muth to  form  insoluble  oxychloride  is  so  strong  that 
the  only  safe  plan  to  pursue  is  to  avoid  its  possibility. 

While  trying  different  methods  of  analysis  on  lead 
bullion,  which  often  contains  over  i%  of  silver,  the 
attempt  was  made  to  remove  most  of  the  silver  at  the 
start  by  adding  a  few  drops  of  hydrochloric  acid  to  the 
sulphuric  acid  used  to  ppt.  the  lead.  While  this  gen- 
erally succeeded,  in  many  cases  bismuth  oxychloride 
was  also  precipitated,  and,  of  course,  lost  with  the  lead 
sulphate  and  silver  chloride;  hence  this  modification 
was  abandoned  as  too  unreliable. 

Along  the  same  line  was  the  attempt  to  remove 
the  silver  and  copper  by  the  use  of  ammonia  (and 
ammonium  carbonate)  as  precipitants  in  the  first 
solution.  In  spite  of  the  utmost  care,  results  obtained 
in  this  way  were  invariably  low.  To  the  mass  action 
of  the  bulky  solution  and  large  amount  of  salts,  the 
loss  of  bismuth  here,  owing  to  incomplete  precipitation, 
is  probably  due. 

When  solutions  have  been  evaporated  to  sulphuric 
acid  fumes,  they  should,  as  soon  as  cool  enough,  be 
diluted,  boiled  and  filtered.  If  such  evaporated  solutions 
are  allowed  to  stand  cold  for  a  few  hours,  or  over  night, 
the  bismuth  is  very  apt  to  separate  in  an  extremely 
soluble  form,  doubtless  as  basic  sulphate,  and  on  sub- 


MILL   AND    SMELTER    METHODS.      125 

sequent  dilution  and  boiling,  fail  to  redissolve.  In 
such  a  case,  of  course,  it  would  be  filtered  off  with  the 
lead  sulphate  and  lost.  Should  this  happen  at  the  first 
evaporation,  where  considerable  lead  sulphate  is  sep- 
arated, it  would  be  completely  masked,  and  could  be 
detected  only  by  analysis  of  the  lead  sulphate.  At  the 
second  evaporation,  where  the  lead  sulphate  separated 
is  generally  so  slight  as  to  be  scarcely  visible,  if  a 
white,  or  yellowish  white,  rather  granular  ppt.  is  no- 
ticed which  seems  insoluble  on  dilution  and  boiling, 
it  is  almost  certain  to  be  a  bismuth  compound.  Pro- 
longed boiling,  with  occasional  decantations  and  addi-. 
tions  of  fresh  portions  of  dilute  sulphuric  acid  will 
generally  affect  its  solution ;  but  both  here  and  at  the 
first  evaporation  there  is  no  danger  of  loss  if  unneces- 
sary delay  is  avoided. 

When  precipitating  with  sodium  carbonate  and  po- 
tassium cyanide  but  a  very  slight  excess  of  the  car- 
bonate solution  should  be  added,  otherwise  precipita- 
tion will  be  incomplete.  Where  this  trouble  is  sus- 
pected it  can  be  corrected  by  the  cautious  addition  of 
ammonium  chloride  until  the  carbonate  is  mostly  con- 
verted to  chloride.  With  proper  care,  however,  the 
necessity  should  not  arise.  In  both  this  precipitation 
and  the  succeeding  one  with  ammonia  and  ammonium 
carbonate  the  solution  should  be  heated  to  boiling,  or 
nearly  so,  until  all  the  free  carbonic  acid  is  expelled 
and  then  allowed  to  stand  in  a  warm  place  until  the 
ppt.  has  thoroughly  collected.  As  both  of  these  ppts. 


126     MILL   AND    SMELTER   METHODS. 

have  a  tendency  to  run  through  the  filter,  fairly  fine- 
textured  papers  should  be  used. 

Where  bismuth  carbonate  is  precipitated  to  ^e 
ignited  and  weighed,  it  must  always  be  done  by  am- 
monia and  ammonium  carbonate  from  a  nitrate  solu- 
tion, and  care  must  be  exercised  to  remove  the  dried 
ppt.  from  the  paper  as  completely  as  possible,  for  re- 
duction and  volatilization  very  readily  take  place.  A 
low  red  heat  is  best  for  igniting  the  carbonate,  the 
change  to  oxide  easily  taking  place.  At  bright  red- 
ness there  is  no  more  loss  in  weight,  but  the  oxide 
fuses  and  is  then  difficult  to  remove  from  the  crucible. 
Bismuth  in  Ores. 

In  ores  carrying  lead  to  the  extent  of  10%  or 
over,  nearly,  if  not  all,  the  bismuth  will  be  found  in 
the  lead  buttons  obtained  in  fire  assay.  And  as  this 
method  of  determining  the  lead  is  the  one  in  common 
use  at  lead  smelters,  and  as  these  buttons  are  being 
constantly  made,  they  can  be  taken  and  the  above 
methods  applied.  In  iron-lead  ores,  by  the  addition 
of  some  bismuth-free  lead  salt — carbonate  or  sulphate 
— the  same  procedure  may  be  followed.  A  number  of 
buttons  from  different  lots  of  the  same  ore  can  be 
mixed  to  represent  an  average  of  a  very  considerable 
amount  of  the  ore.  Or,  owing  to  the  presence  of  anti- 
mony or  arsenic,  these  buttons  can  be  scorified  to- 
gether with  the  addition  of  some  silica  and  borax  glass, 
the  loss  of  bismuth  in  a  short  scorification  being  very 
small. 


MILL   AND   SMELTER   METHODS.      127 

Of  course  this  method  is  not  very  accurate,  but  it 
serves  the  purpose  of  informing  the  metallurgist  what 
ores  the  bismuth  is  coming  from  so  that  he  may  avoid 
them  as  far  as  possible  in  his  operations.  In  the  re- 
finery, bullion  carrying  much  bismuth  is  run  sepa- 
rately, such  bullion  being  all  right  for  shot  or  pipe 
but  not  fit  for  corroding  purposes. 
Determination  of  Copper  in  Silver  Mud  and  Silver 

Mill  Slags. 

Treat  -J  gram  with  5  cc.  HNO3,  and,  when  action 
has  become  quiet,  add  3  cc.  H2SO4,  and  evaporate  to 
white  fumes ;  cool,  add  50  cc.  H2O,  and  heat  to  dis- 
solve the  soluble  sulphates ;  add  NaCl  solution  in 
slight  excess,  heat  to  boiling,  remove  and  filter  off  the 
AgCl.  To  the  filtrate  add  sodium  sulphite  and  a 
small  excess  of  NH4CNS,  stir  and  warm;  Cu2(CNS)2 
will  precipitate ;  filter,  wash  thoroughly,  ignite  gently 
in  a  porcelain  crucible.  Dissolve  the  residue  in  5  cc. 
HNO3,  and  determine  Cu  electrolytically. 

Slags. 

Treat  i  gram  in  a  Pt  dish  with  6  cc.  HNO3  and  6 
cc.  HF.    Add  4  cc.  H2SO4,  and  proceed  as  before. 
Silver  Determination  on  Anode  Copper  by  Fire  Assay. 

The  silver  is  pptd.  as  AgCl,  scorified  and  cupelled. 

Weigh  i  A.  T.  of  the  sample  in  duplicate,  place  in 
a  large  beaker,  add  200  cc.  cold  water  +130  cc.  HNOn 
and  let  stand  until  completely  dissolved.  Then  add 
175  cc.  of  cold  water  and  8  cc,  NaCl  sol,  (i  cc.  equals 


128     MILL   AND    SMELTER    METHODS. 

184  mgs.).  Stir  the  solution  well  for  a  few  minutes 
and  allow  to  stand  for  twelve  hours,  to  allow  AgCl 
to  settle.  Filter  and  wash,  add  a  couple  of  grams  of 
litharge  and  set  the  filter  paper  on  a  2^-inch  scorifier, 
place  in  a  muffle  and  burn  off  the  filter  paper  at  a  very 
low  temperature.  Take  the  scorifier  from  the  muffle 
and  add  about  35  grams  of  lead  with  4  grams  of  borax 
for  a  cover.  Place  the  scorifier  in  the  muffle  at  a 
cherry  red  heat  and  scoriiy^at  a  low  temperature.  This 
gives  about  an  1 8-gram  button.  Cupel  and  weigh. 

Bismuth  in  Metallic  Copper. 

Dissolve  10  to  50  grams  of  the.  copper  in  HNO3  and 
H2O.  If  much  insoluble  matter  is  present,  filter  off 
and  fuse  it  with  Na2CO3.  Dissolve  the  fusion  in  HNO3 
and  add  to  main  solution.  To  the  solution  in  HNO3 
add  Na2CO3  until  a  slight  permanent  precipitate  is 
formed.  All  the  Bi  will  be  included  in  this  ppt.  Fil- 
ter it  from  the  main  solution,  dissolve  the  ppt.  from 
the  filter  with  warm  dilute  HC1.  Evaporate  the  HC1 
solution  on  a  water  bath  till  free  acid  is  driven  off, 
then  add  five  or  six  drops  acid  and  2  or  3  cc.  of  water. 
The  solution  should  be  clear — if  not,  add  a  few  drops 
HCI  to  clarify,  then  pour  into  the  solution  a  large 
volume  of  water  (400  to  500  cc.),  and  let  the  ppt.  of 
BiOCl  separate  over  night.  Weigh  as  BiOCl  on 
Gooch  crucible. 

Electrolytic  Copper  Determination. 
Copper — All   samples  containing  more  than  2  or 


MILL   AND    SMELTER    METHODS.      129 

3%  copper,  such  as  mattes,  ores,  copper  cakes,  etc.,  are 
run  for  copper  by  the  electrolytic  method,  as  follows : 

Weigh  out  from  -J  to  I  gram  of  ore  in  a  No.  3 
beaker;  just  moisten  with  a  drop  or  two  of  water, 
then  add  from  10  to  15  cc.  of  strong  nitric  acid,  and  5 
to  8  cc.  of  sulphuric  acid,  and  heat  until  white  fumes 
of  sulphuric  acid  are  given  off.  Be  sure  that  all  of 
the  ore  (which  is  soluble  in  acids)  has  been  dissolved, 
then  dilute  to  about  80  cc.rheat  again  just  to  boiling, 
to  distintegrate  the  mass ;  filter  off  the  residue  in  which 
the  lead  and  silica  may  be  determined  if  necessary. 
Filter  the  solution  into  a  No.  2  beaker,  add  i  or  2 
strips  of  heavy  aluninum  foil,  boil  for  ten  or  fifteen 
minutes,  which  is  generally  sufficient  to  insure  com- 
plete precipitation  of  the  copper.  Pour  off  the  solu- 
tion and  wash  three  times  by  decantation  with  hot 
water.  Then  add  3  or  4  cc.  of  strong  nitric  acid  to 
the  contents  of  the  beaker,  allowing  the  acid  to  flow 
over  the  aluminum.  Boil  to  expel  the  nitrous  fumes, 
decant  into  another  beaker  (a  long,  narrow  one)  and 
rinse  the  aluminum  with  a  few  drops  of  water ;  just 
neutralize  the  solution  with  ammonia,  and  add  about 
15  cc.'s  of  i  to  10  sulphuric  acid.  Place  platinum 
cylinder  into  the  solution,  connecting  it  with  the  neg- 
ative or  zinc  element  of  the  battery ;  inside  the  cylinder 
place  a  platinum  wire  spiral,  reaching  almost  to  the 
bottom  of  the  beaker,  being  careful  not  to  allow  the 
spiral  to  touch  the  cylinder. 

A  very  good  battery  for  this  purpose  is  a  Bunsen 


130     MILL   AND   SMELTER    METHODS. 

cell ;  about  eight  hours  is  usually  required  for  a  total 
precipitation  of  the  copper.  To  determine  whether  or 
not  all  the  copper  has  been  pptd.,  remove  a  few  drops 
of  the  solution  in  a  pipette  and  test  it  with  H2S  water. 
If  the  test  shows  that  all  copper  has  been  removed, 
then,  without  turning  off  the  current,  remove  the  cyl- 
inder and  place  immediately  into  a  beaker  of  warm 
water,  so  as  to  wash  off  as  quickly  as  possible  all  acid 
from  the  cylinder.  After  the  cylinder  has  been  thor- 
oughly washed,  place  it  in  a  beaker  of  alcohol,  which 
removes  the  water,  then  dry  as  quickly  and  carefully 
as  possible,  avoiding  the  oxidation  of  the  copper  on 
the  cylinder.  The  pptd.  copper  should  be  a  bright, 
rose-red  color. 

In  case  the  ore  contains  only  a  trace  of  arsenic, 
antimony  or  bismuth,  the  precipitation  of  the  copper 
on  the  aluminum  foil  may  be  dispensed  with.  In  that 
case,  after  the  ore  has  been  dissolved  and  the  mass 
disintegrated,  add  enough  ammonia  to  just  neutralize 
this  solution,  add  ^  gram  NH4NO3  and  15  cc.  of  i  to 
10  H2SO4,  and  place  on  the  battery  as  before. — From 
Chemists'  Handbook,  Western  Chemical  Company. 


MILL   AND   SMELTER    METHODS.      131 


CHAPTER  XI. 


The   Laboratory. 


In  technical  laboratories,  where  quick  and  accu- 
rate work  is  required,  the  general  arrangement  and 
convenience  of  the  laboratory  itself  is  of  the  greatest 
importance  ;  so  a  word  or  two  about  the  general  equip- 
ment will  not  be  out  of  place  in  this  book.  The  aver- 
age chemist  will  be  called  on  for  from  forty  to  eighty 
determinations  a  day,  varying  from  silica,  iron  and 
lime  to  antimony,  arsenic  and  even  an  occasional  rare 
element,  yet  the  greater  part  of  the  work  can  be  so 
arranged  that  all  ores  and  mattes,  etc.,  requiring  the 
same  elements  determined  can  be  run  together,  thus 
making  little  more  work  for  ten  samples  than  is  re- 
quired for  two.  To  facilitate  this  arrangement  ample 
heating  space,  filter  racks,  and  hot,  distilled  water 
must  be  provided,  and  space  so  economized  that  no 
unnecessary  steps  are  required  in  moving  from  one 
piece  of  apparatus  to  another.  The  best  plan  for  such 
a  laboratory  is  as  follows : 

The  laboratory  should  consist  of  two  rooms  con- 
nected by  a  swinging  door,  one  room  being  considerably 
larger  than  the  other.  The  larger  room  will  contain 
the  hot  plate,  the  filtering  stands,  the  burette  stands, 
water  condenser,  etc.,  while  the  smaller  room  will  con- 


132     MILL   AND   SMELTER    METHODS. 

tain  the  balances,  reserve  chemicals  and  apparatus  and 
will  be  used  as  a  sort  of  office.  Both  of  these  rooms 
should  be  well  lighted  and  the  larger  room  should  be 
provided  with  ample  ventilation,  preferably  by  means 
of  a  skylight. 

The  Hot  Plate. — This  consists  of  a  stand  of  sheet 
iron  raised  about  four  inches  above  the  flame  and  on 
top  of  which  is  laid  a  sheet  of  J-inch  asbestos.  The 
best  size  for  the  top  is.  4  feet  in  length  by  2\  feet 
in  width,  and  such  a  top  will  require  four  gasoline 
burners  to  heat  it.  In  many  plants,  gasolene  is  not 
used  and  a  very  good  substitute  is  found  in  the  ordi- 
nary four-hole  coal  oil  stove.  In  other  plants  a  coal 
fire  under  a  heavy  cast  iron  plate  protected  by  fire 
brick  has  been  tried,  but  the  results  are  not  satis- 
factory. 

The  hot  plate  should  be  surmounted  by  a  hood, 
preferably  of  brick  built  up  in  the  manner  of  the  old- 
fashioned  fire-place  and  terminating  in  a  chimney  of 
sufficient  height  to  furnish  ample  draught.  The  top 
of  the  plate  should  be  3^  feet  above  the  level  of  the 
floor. 

At  the  Selby  Plant  electric  stoves  are  used.  These 
have  a  No.  10  steel  plate  i8"xi4"xi"  for  a  top;  con- 
tain two  circuits  of  No.  16  climax  wire  in  parallel,  52 
feet  of  wire  in  each  circuit,  wound  on  a  5/16"  rod. 
Each  circuit  no  volts,  *j\  amperes.  Temperature  ap- 
proximately 150  degrees  C. 

Filter  Racks. — These  should  be  of  wood  and  be 


MILL   AND   SMELTER    METHODS.      133 

fastened  to  a  table  running  lengthwise  of  the  room 
and  parallel  to  the  hot  plate.  Space  should  be  ar- 
ranged for  twenty  funnels  in  all  and  these  should  be 
selected  with  care  so  as  to  have  all  alike,  then  the  filter 
paper  will  always  fit  and  filtering  will  be  rapid.  Above 
the  table  at  a  height  of  two  feet  above  the  top  of  the 
funnels  will  be  placed  a  reservoir  containing  five  gal- 
lons of  distilled  water  which  is  kept  boiling  by  a 
flame  underneath.  A  rubber  tube  of  sufficient  length 
to  reach  to  each  end  of  the  filter  rack  is  connected 
to  the  reservoir,  ample  wash  water  being  thus  supplied. 
But  one  step  should  be  necessary  in  taking  a  beaker 
from  the  plate  to  the  filter  rack. 

Burette  Stand. — On  the  opposite  side  of  the  room 
and  preferably  in  front  of  a  window,  should  be  placed 
the  burette  stand.  The  best  arrangement  of  this  kind 
was  designed  by  Mr.  E.  M.  Johnson,  and  was  in  use 
in  the  Grant  smelter  in  Denver.  The  burettes  were 
held  in  position  against  an  upright  frame  work  by 
means  of  wire  bird  cage  springs  while  the  solutions 
were  placed  on  a  shelf  underneath  the  table.  Connec- 
tion was  made  between  the  burette  and  the  solution  by 
means  of  three-way  cock  and  a  glass  tube  running 
from  this,  through  the  table  and  down  to  the  bottom 
of  the  solution  bottle.  Through  another  tube  air  was 
forced  into  the  bottle,  thus  causing  the  solution  to  rise 
in  the  burette.  A  turn  of  the  cock  shuts  off  the  supply 
when  the  burette  was  full,  another  turn  would  release 
the  solution  when  titrating,  and  still  another  turn. 


134     MILL   AND   SMELTER   METHODS. 

when  the  titration  was  completed,  would  allow  the  ex- 
cess of  solution  to  return  to  the  bottle  below.  The  top 
of  the  table  underneath  the  spout  of  the  burette  was 


covered  with  a  plate  of  glass  underneath  which  was 
placed  a  sheet  of  white  glazed  paper. 


MILL   AND    SMELTER    METHODS.      135 

With  such  an  apparatus,  with  separate  burettes 
for  each  of  the  standard  solutions  in  daily  use,  the 
time  required  in  titrating  is  cut  down  to  almost  noth- 
ing. For  ease  in  removing  an  empty  solution  bottle 
and  replacing  with  a  full  one,  the  connection  between 
the  glass  tube  and  the  burette  is  made  with  a  small 
piece  of  rubber  tubing.  By  slipping  this  off,  drawing 
the  tube  up  through  the  table,  etc.,  the  exchange  is 
easily  made. 

The  advantages  of  this  arrangement  are :  No  rub- 
ber tubes  to  burst  and  release  the  solution,  as  is  the 
case  when  the  burette  is  filled  by  gravity ;  no  solution 
allowed  to  remain  in  the  burette  exposed  to  the  light 
when  not  in  use;  and  the  fact  that  the  burettes  are 
always  ready  for  business. 

Distilled  Water. — The  best  apparatus  for  distilling 
water  for  laboratory  use,  provided  steam  can  be  ob- 
tained, is  the  following:  A  cylindrical  tank  four  feet 
in  height,  made  of  three  sections  fitting  together,  each 
section  being  made  of  ^-inch  copper  sheet.  In  the 
top  section  steam  at  ninety  pounds'  pressure  circulates 
in  a  copper  spiral,  which  is  generally  protected  with 
tin.  Cold  water  surrounds  this  spiral,  and  the  steam 
produced  is  led  off  at  the  top  in  a  tin-lined  pipe  and 
passed  through  a  spiral  pipe  surrounded  by  running 
cold  water  in  the  second  section.  The  condensed  water 
then  drops  into  the  third  or  bottom  section.  Taps  are 
placed  just  above  the  bottom  of  each  section  to  provide 
a  means  of  washing  out  the  sediment  at  certain  inter- 


136     MILL   AND    SMELTER   METHODS. 

vals.  Such  a  still,  with  each  section  18  inches  high 
and  12  inches  in  diameter,  will  furnish  one-half  gal- 
lon per  hour  of  distilled  water. 

Balances. — There  should  be  two  balances,  one  for 
weighing  pulp  and  one  for  analytical  work.  These 
should  be  placed  on  a  firm  table,  with  ample  room 
allowed  on  each  side  for  samples  and  for  the  beakers 
or  casseroles  into  which  the  material  is  to  be  weighed. 

Having  such  a  laboratory,  the  day's  work  would 
proceed  as  follows:  First  of  all,  the  fires  are  started 
and  the  receptacle  for  distilled  water  is  filled ;  then 
the  still  is  started  and  regulated,  if  it  so  happens  that 
the  supply  of  water  is  low.  Next  the  chemist  goes  to 
the  balance  room  and  arranges  the  samples  that  are 
to  be  analyzed  in  proper  order  on  the  lefthand  side  of 
the  pulp  balance.  Then  he  returns  to  the  other  room 
and  selects  the  necessary  beakers  and  casseroles  and 
arranges  them  on  a  flat  wooden  tray.  Placing  this 
tray  on  the  right  side  of  the  balance,  he  proceeds  to 
weigh  up,  throwing  the  samples  to  one  side  as  he  fin- 
ishes them.  Taking  his  tray,  he  now  proceeds  to  a 
small  table  at  the  left  of  the  hot  plate,  where  the  acid 
bottles,  etc.,  are  kept.  The  acids  are  added  and  the 
samples  placed  on  the  hot  plate.  While  waiting  for 
the  samples  to  boil  the  chemist  puts  the  samples  of 
ore  away  in  regular  order,  for  they  will  be  needed 
again  later  on  for  mixture  beds,  prepares  the  filter  pa- 
pers, etc.,  and  in  general  gets  everything  ready  for  in- 
stant service,  From  this  time  on  the  work  follows  a 


MILL   AND   SMELTER   METHODS.      137 


definite  system  and  the  only  pauses   in   this   regular 
rush  of  work  come  when  it  is  necessary  to  go  out  to 

STILL 


Top  for  C/eap/yo  Out 
Water  QuMet 


Wafer 


the  fire  room  to  use  a  muffle.     By  noon  the  worst  of 
the  work  is  over,  so  the  afternoons  are  usually  spent 


138     MILL   AND   SMELTER    METHODS. 

on  some  unusual  work,  or  in  standardizing  solutions, 
etc.,  and  in  preparing  for  the  work  of  the  following 
day. 

Among  the  minor  pieces  of  apparatus  which  are 
found  to  be  of  use  in  the  laboratory,  the  following  in 
particular  may  be  mentioned.  It  consists  of  a  -J-litre 


/7L  7E/?//v(j- 


Perforated 
P/*t,n<jm  DISH 
fuaeof  Into  Class 

flask  fitted  with  a  rubber  cork  through  which  pass  two 
pieces  of  glass  tube,  reaching  just  through  the  cork. 
One  piece,  bent  in  the  shape  of  the  letter  U,  reaches 
down  on  the  outside  to  within  \  an  inch  of  the  table, 
having  the  end  spread  and  a  piece  of  perforated  plat- 


MILL   AND    SMELTER    METHODS.      139 

inum  inserted  and  the  glass  melted  around  it  to  hold 
it  in  place.  The  other  piece  of  tubing  merely  serves  to 
attach  the  tube  from  a  suction  pump.  In  another 
flask  is  placed  some  shreds  of  asbestos  covered  with 
water.  For  such  operations  as  filtering  off  the  solu- 
tion when  the  copper  has  been  precipitated  on  alumi- 
num foil,  this  apparatus  is  a  great  time  saver.  The 
flask  is  connected  to  the  suction  pump  and  then  dipped 
into  the  asbestos.  The  asbestos  will  cover  the  plati- 
num with  a  fine  coat  which  will  prevent  the  passage  of 
fine  particles  of  solid  matter,  but  will  allow  the  solu- 
tion to  pass  freely.  When  coated,  the  tube  is  trans- 
ferred to  the  solution  to  be  filtered. 


140     MILL   AND    SMELTER    METHODS. 


Miscellaneous. 


The  Assay  Ton  System. 

i  Ib.  avoirdupois  equals  7,000  grains. 

2,000  Ibs.  avoirdupois  equals  I  ton. 

2,000x7,000  equals  14,000,000  troy  grains  in  I  ton 
avoirdupois. 

480  troy  grains  equals  I  ounce  troy. 

14,000,000/480  equals  29,166  troy  ounces  in  2,000 
Ibs.  avoirdupois. 

There  are  29,166  milligrammes  in  i  assay  ton  (A. 
T.),  hence— 

2,000  Ibs.  :  i  A.  T.  : :  i  ounce  troy  :  i  milligramme. 

Impurities  in  C.  P.  Acids. 
Hydrochloric  Acid — 

For  iron,  dilute,  and  add  KSCN ;  if  it  shows  a  red 
color,  there  is  iron  present. 

For  arsenic,  dilute,  pass  in  hydrogen  sulphide 
gas;  if  a  distinct  yellow  precipitate  is  obtained,  it 
would  indicate  traces  of  arsenic ;  also  try  by  the  Marsh 
test. 

For  sulphuric   acid,   dilute,  add  barium  chloride ; 
a   white   precipitate   would   be   obtained   if   sulphuric 
acid  were  present. 
Nitric  Acid — 

For  chlorine,  add  silver  nitrate;  if  a  slight  opal- 
esence  occurs,  it  shows  the  presence  of  chlorine. 


MILL  AND   SMELTER  METHODS.      141 

Sulphuric  Acid — 

For  arsenic,  dilute  and  pass  in  hydrogen  sulphide 
gas ;  if  a  distinct  yellow  precipitate  is  the  result,  it 
shows  the  presence  of  arsenic ;  also  try  by  the  Marsh 
test. 

For  iron,  dilute,  add  KSCN ;   if  red  color  appears, 
it  shows  presence  of  iron. 
Ammonia — 

For  organic  matter,  dilute,  acidify  with  nitric 
acid ;  if  a  red  color  appears,  it  shows  the  presence  of 
organic  matter.  After  acidifying  with  nitric  acid, 
add  barium  chloride ;  if  a  white  precipitate  is  obtained, 
it  shows  the  presence  of  sulphuric  acid. 

In  making  these  tests  be  sure  that  all  the  apparatus 
is  clean  and  be  sure  that  the  distilled  water  contains 
no  impurities. 


International    Atomic    Weights. 


Aluminum Al         27.1  26.9 

Antimony Sb  120.2  119.3 

Argon A          39.9  39.6 

Arsenic As         75.0  744 

Barium Ba  137.4  136.4 

Bismuth   Bi  208.5  206.9 

Boron  B  1 1  10.9 

Bromine Br         79.96  79.36 

Cadmium  Cd  112.4  m.6 

Caesium   Cs  133  132 


•142      MILL  AND   SMELTER  METHODS. 

Calcium Ca  40.1  39.8 

Carbon  C  12.00  11.91 

Cerium Ce  140  139 

Chlorine  Cl  35,45  35.18 

Chromium Cr  52.1  51.7 

Cobalt Co  59.0  58.56 

Columbium  (Niobium)  Cb  94  93.3 

Copper Cu  63.6  63.1 

Erbium E  166  164.8 

Fluorine F  19  18.9 

Gadolinium Gd  156  155 

Gallium Ga  70  69.5 

Germanium Ge  72.5  71.9 

Glucinium  (Beryllium)   Gl  9.1  9.03 

Gold Au  197.2  195.7 

Helium He          4  4 

Hydrogen H  i  .008         1 .000 

Indium In  114  1 13.1 

Iodine I  126.85  I25-9° 

Iridium   Ir  193.0  !9!-5 

Iron   Fe  55.9  55.5 

Krypton  K  81.8  81.2 

Lanthanum La  138.9  l37-9 

Lead Pb  206.9  2O5-35 

Lithium    . Li  7.03  6.98 

Magnesium Mg  24.36  24.18 

Manganese  Mn  55.0  54.6 

Mercury    Hg  200.0  198.5 

Molybdenum  ..............   Mo  96.0  95.3 


MILL  AND   SMELTER   METHODS.      143 

Neodymium    Ne  143.6  142.5 

Neon   20  19.9 

Nickel   Ni         58.7  58.3 

Nitrogen N          14.04  13.93 

Osmium Os  191  189.6 

Oxygen '.  O           16.00  15.88 

Palladium   Pd  106.5  IO5-7 

Phosphorus   P           31.0  30.77 

Platinum Pt  194.8  193-3 

Potassium « K          39-15  38.86 

Praseodymium Pr  140.5  J39-4 

Radium Ra  252  223.3 

Rhodium Rh  103.0  102.2   ' 

Rubidium    Rb        85.4  84.8 

Ruthenium Ru  101.7  100.9 

Samarium Sm  150  148.9 

Scandium Sc         44.1  43.8 

Selenium Se         79.2  78.6 

Silicon Si          28.4  28.2 

Silver   Ag  107.93  107.12 

Sodium Na        23.05  22.88 

Strontium Sr          87.6  86.94 

Sulphur S           32.06  31.83 

Tantalum Ta  183  181.6 

Tellurium Te  127.6  126.6 

Terbium Tb  160  158.8 

Thallium  Tl  204.1  202.6 

Thorium Th  232.5  230.8 

Thulium Tm  171  169.7 


144      MILL  AND   SMELTER  METHODS. 

Tin Su  119.0  118.1 

Titanium    Ti  48.1  47.7 

Tungsten   W  184.0  182.6 

Uranium U  238.5  236.7 

Vanadium    V  51.2  50.8 

Xenon ....:....    X  128  127 

Ytterbium  Yb  173.0  171.7 

Yttrium Yt  89.0  88.3 

Zinc  Zn  65.4  64.9 

Zirconium  . Zr  90.6  89.9 


$^l 

Al^Jii* 


fif 

®£f£i 


m  ru  '895; 


36483? 


T/V 
A  7 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


